Oracle 10g sql fundamentals i

Oracle Database 10g: SQL
Fundamentals I

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August 2004
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Introduction

Copyright © 2004, Oracle. All rights reserved.

Lesson Objectives

After completing this lesson, you should be able to do
the following:
• List the features of Oracle10g
• Discuss the theoretical and physical aspects of a
relational database
• Describe the Oracle implementation of the RDBMS
and ORDBMS
• Understand the goals of the course


Goals of the Course

After completing this course, you should be able to do
the following:
• Identify the major structural components of
Oracle Database 10g
• Retrieve row and column data from tables with the
SELECT statement
• Create reports of sorted and restricted data
• Employ SQL functions to generate and retrieve
customized data
• Run data manipulation language (DML) statements
to update data in Oracle Database 10g
• Obtain metadata by querying the dictionary views


Oracle10g

One
Scalability
vendor

Unified
Reliability
management

Single
Common
development
skill sets
model


Oracle10g


Oracle Database 10g

Object relational data

Documents

Multimedia

Messages


Oracle Application Server 10g

Portals

Transactional applications

Business intelligence

Integration

Application Application
development server
framework


Oracle Enterprise Manager 10g
Grid Control

• Software provisioning
• Application service level monitoring


Relational and Object Relational
Database Management Systems

• Relational model and object relational model
• User-defined data types and objects
• Fully compatible with relational database
• Support of multimedia and large objects
• High-quality database server features


Oracle Internet Platform
Clients

Any Any Any
browser mail client FTP client

Development tools
System management

Internet applications
SQL
Business logic Presentation and
and data business logic
PL/SQL

Databases Application
servers Java

Network services


System Development Life Cycle

Strategy
and
analysis
Design
Build
and
document
Transition

Production


Data Storage on Different Media

Electronic Database
spreadsheet Filing cabinet


Relational Database Concept

• Dr. E. F. Codd proposed the relational model for
database systems in 1970.
• It is the basis for the relational database
management system (RDBMS).
• The relational model consists of the following:
– Collection of objects or relations
– Set of operators to act on the relations
– Data integrity for accuracy and consistency


Definition of a Relational Database

A relational database is a collection of relations or
two-dimensional tables.
Oracle
server

Table name: EMPLOYEES Table name: DEPARTMENTS

… …


Data Models

Model of
system
Entity model of
in client’s
client’s model
mind
Table model
of entity model Oracle
server

Tables on disk


Entity Relationship Model

• Create an entity relationship diagram from
business specifications or narratives:

EMPLOYEE DEPARTMENT
assigned to
#* number #* number
* name * name
o job title composed of o location

• Scenario
– “. . . Assign one or more employees to a
department . . .”
– “. . . Some departments do not yet have assigned
employees . . .”


Entity Relationship
Modeling Conventions

Entity Attribute
• Singular, unique name • Singular name
• Uppercase • Lowercase
• Soft box • Mandatory marked with *
• Synonym in parentheses • Optional marked with “o”

EMPLOYEE DEPARTMENT
#* number assigned to
#* number
* name * name
o job title composed of o location

Unique identifier (UID)
Primary marked with “#”
Secondary marked with “(#)”


Relating Multiple Tables

• Each row of data in a table is uniquely identified
by a primary key (PK).
• You can logically relate data from multiple tables
using foreign keys (FK).

Table name: DEPARTMENTS
Table name: EMPLOYEES

…
Primary key Foreign key Primary key


Relational Database Terminology

3 4
2

5

6

1


Relational Database Properties

A relational database:
• Can be accessed and modified by executing
structured query language (SQL) statements
• Contains a collection of tables with no physical
pointers
• Uses a set of operators


Communicating with an RDBMS
Using SQL

SQL statement is entered. Statement is sent to
Oracle server.
SELECT department_name
FROM departments;
Oracle
server


Oracle’s Relational Database Management
System

Oracle
server

User tables Data
dictionary


SQL Statements
SELECT
INSERT
UPDATE Data manipulation language (DML)
DELETE
MERGE

CREATE
ALTER
DROP Data definition language (DDL)
RENAME
TRUNCATE
COMMENT

GRANT Data control language (DCL)
REVOKE

COMMIT
ROLLBACK Transaction control
SAVEPOINT


Tables Used in the Course

EMPLOYEES

DEPARTMENTS JOB_GRADES


Summary

• Oracle Database 10g is the database for grid
computing.
• The database is based on the object relational
database management system.
• Relational databases are composed of relations,
managed by relational operations, and governed
by data integrity constraints.
• With the Oracle server, you can store and manage
information by using the SQL language and
PL/SQL engine.


Retrieving Data Using
the SQL SELECT Statement


Objectives

the following:
• List the capabilities of SQL SELECT statements
• Execute a basic SELECT statement
• Differentiate between SQL statements and
iSQL*Plus commands


Capabilities of SQL SELECT Statements

Projection Selection

Table 1 Table 1

Join

Table 1 Table 2


Basic SELECT Statement

SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;

• SELECT identifies the columns to be displayed
• FROM identifies the table containing those columns


Selecting All Columns

SELECT *
FROM departments;


Selecting Specific Columns

SELECT department_id, location_id
FROM departments;


Writing SQL Statements

• SQL statements are not case-sensitive.
• SQL statements can be on one or more lines.
• Keywords cannot be abbreviated or split
across lines.
• Clauses are usually placed on separate lines.
• Indents are used to enhance readability.
• In iSQL*Plus, SQL statements can optionally be
terminated by a semicolon (;). Semicolons are
required if you execute multiple SQL statements.
• In SQL*plus, you are required to end each SQL
statement with a semicolon (;).


Column Heading Defaults

• iSQL*Plus:
– Default heading alignment: Center
– Default heading display: Uppercase
• SQL*Plus:
– Character and Date column headings are left-
aligned
– Number column headings are right-aligned
– Default heading display: Uppercase


Arithmetic Expressions

Create expressions with number and date data by
using arithmetic operators.
Operator Description
+ Add
- Subtract
* Multiply
/ Divide


Using Arithmetic Operators

SELECT last_name, salary, salary + 300
FROM employees;

…


Operator Precedence

SELECT last_name, salary, 12*salary+100
FROM employees; 1

…
SELECT last_name, salary, 12*(salary+100)
FROM employees;
2

…


Defining a Null Value

• A null is a value that is unavailable, unassigned,
unknown, or inapplicable.
• A null is not the same as a zero or a blank space.
SELECT last_name, job_id, salary, commission_pct
FROM employees;

…

…


Null Values
in Arithmetic Expressions

Arithmetic expressions containing a null value
evaluate to null.
SELECT last_name, 12*salary*commission_pct
FROM employees;

…

…


Defining a Column Alias

A column alias:
• Renames a column heading
• Is useful with calculations
• Immediately follows the column name (There can
also be the optional AS keyword between the
column name and alias.)
• Requires double quotation marks if it contains
spaces or special characters or if it is case-
sensitive


Using Column Aliases

SELECT last_name AS name, commission_pct comm
FROM employees;

…

SELECT last_name "Name" , salary*12 "Annual Salary"
FROM employees;

…


Concatenation Operator

A concatenation operator:
• Links columns or character strings to other
columns
• Is represented by two vertical bars (||)
• Creates a resultant column that is a character
expression
SELECT last_name||job_id AS "Employees"
FROM employees;

…


Literal Character Strings

• A literal is a character, a number, or a date that is
included in the SELECT statement.
• Date and character literal values must be enclosed
by single quotation marks.
• Each character string is output once for each
row returned.


Using Literal Character Strings

SELECT last_name ||' is a '||job_id
AS "Employee Details"
FROM employees;

…


Alternative Quote (q) Operator

• Specify your own quotation mark delimiter
• Choose any delimiter
• Increase readability and usability
SELECT department_name ||
q'[, it's assigned Manager Id: ]'
|| manager_id
AS "Department and Manager"
FROM departments;

…


Duplicate Rows

The default display of queries is all rows, including
duplicate rows.
SELECT department_id
FROM employees; 1

…
SELECT DISTINCT department_id
FROM employees; 2

…


SQL and iSQL*Plus Interaction

SQL statements
Oracle
server
Internet
browser

iSQL*Plus Query results
commands

Formatted report
Client


SQL Statements Versus
iSQL*Plus Commands
SQL iSQL*Plus
• A language • An environment
• ANSI standard • Oracle-proprietary
• Keyword cannot be • Keywords can be
abbreviated abbreviated
• Statements manipulate • Commands do not allow
data and table definitions manipulation of values in
in the database the database
• Runs on a browser
• Centrally loaded; does not
have to be implemented
on each machine

SQL iSQL*Plus
statements commands


Overview of iSQL*Plus

After you log in to iSQL*Plus, you can:
• Describe table structures
• Enter, execute, and edit SQL statements
• Save or append SQL statements to files
• Execute or edit statements that are stored in
saved script files


Logging In to iSQL*Plus

From your browser environment:


iSQL*Plus Environment
8 9

7

1
6

2 3 4 5


Displaying Table Structure

Use the iSQL*Plus DESCRIBE command to display the
structure of a table:

DESC[RIBE] tablename



DESCRIBE employees


Interacting with Script Files

SELECT last_name, hire_date, salary
FROM employees; 1

2



1



D:TEMPemp_data.sql

2
3


iSQL*Plus History Page

3

2

1


iSQL*Plus History Page

3

4


Setting iSQL*Plus Preferences

1

2
3


Setting the Output Location Preference
2

1


Summary

In this lesson, you should have learned how to:
• Write a SELECT statement that:
– Returns all rows and columns from a table
– Returns specified columns from a table
– Uses column aliases to display more descriptive
column headings
• Use the iSQL*Plus environment to write, save, and
execute SQL statements and iSQL*Plus
commands
FROM table;


Practice 1: Overview

This practice covers the following topics:
• Selecting all data from different tables
• Describing the structure of tables
• Performing arithmetic calculations and specifying
column names
• Using iSQL*Plus


Restricting and Sorting Data


Objectives

the following:
• Limit the rows that are retrieved by a query
• Sort the rows that are retrieved by a query
• Use ampersand substitution in iSQL*Plus to
restrict and sort output at run time


Limiting Rows Using a Selection

EMPLOYEES

…

“retrieve all
employees in
department 90”


Limiting the Rows That Are Selected

• Restrict the rows that are returned by using the
WHERE clause:
FROM table
[WHERE condition(s)];

• The WHERE clause follows the FROM clause.


Using the WHERE Clause

SELECT employee_id, last_name, job_id, department_id
FROM employees
WHERE department_id = 90 ;


Character Strings and Dates

• Character strings and date values are enclosed by
single quotation marks.
• Character values are case-sensitive, and date
values are format-sensitive.
• The default date format is DD-MON-RR.

SELECT last_name, job_id, department_id
FROM employees
WHERE last_name = 'Whalen' ;


Comparison Conditions

Operator Meaning
= Equal to
> Greater than
>= Greater than or equal to
< Less than
<= Less than or equal to
<> Not equal to
BETWEEN Between two values
...AND... (inclusive)
IN(set) Match any of a list of values
LIKE Match a character pattern
IS NULL Is a null value


Using Comparison Conditions

SELECT last_name, salary
FROM employees
WHERE salary <= 3000 ;


Using the BETWEEN Condition

Use the BETWEEN condition to display rows based on a
range of values:
SELECT last_name, salary
FROM employees
WHERE salary BETWEEN 2500 AND 3500 ;

Lower limit Upper limit


Using the IN Condition

Use the IN membership condition to test for values in
a list:
SELECT employee_id, last_name, salary, manager_id
FROM employees
WHERE manager_id IN (100, 101, 201) ;


Using the LIKE Condition

• Use the LIKE condition to perform wildcard
searches of valid search string values.
• Search conditions can contain either literal
characters or numbers:
– % denotes zero or many characters.
– _ denotes one character.

SELECT first_name
FROM employees
WHERE first_name LIKE 'S%' ;


Using the LIKE Condition

• You can combine pattern-matching characters:
SELECT last_name
FROM employees
WHERE last_name LIKE '_o%' ;

• You can use the ESCAPE identifier to search for the
actual % and _ symbols.


Using the NULL Conditions

Test for nulls with the IS NULL operator.
SELECT last_name, manager_id
FROM employees
WHERE manager_id IS NULL ;


Logical Conditions

Operator Meaning
AND Returns TRUE if both component
conditions are true
OR Returns TRUE if either component
condition is true
NOT Returns TRUE if the following
condition is false


Using the AND Operator

AND requires both conditions to be true:
SELECT employee_id, last_name, job_id, salary
FROM employees
WHERE salary >=10000
AND job_id LIKE '%MAN%' ;


Using the OR Operator

OR requires either condition to be true:
FROM employees
WHERE salary >= 10000
OR job_id LIKE '%MAN%' ;


Using the NOT Operator

SELECT last_name, job_id
FROM employees
WHERE job_id
NOT IN ('IT_PROG', 'ST_CLERK', 'SA_REP') ;


Rules of Precedence

Operator Meaning
1 Arithmetic operators
2 Concatenation operator
3 Comparison conditions
4 IS [NOT] NULL, LIKE, [NOT] IN
5 [NOT] BETWEEN
6 Not equal to
7 NOT logical condition
8 AND logical condition
9 OR logical condition

You can use parentheses to override rules of precedence.


Rules of Precedence

SELECT last_name, job_id, salary
FROM employees
WHERE job_id = 'SA_REP' 1
OR job_id = 'AD_PRES'
AND salary > 15000;

FROM employees
WHERE (job_id = 'SA_REP' 2
OR job_id = 'AD_PRES')
AND salary > 15000;


Using the ORDER BY Clause

• Sort retrieved rows with the ORDER BY clause:
– ASC: ascending order, default
– DESC: descending order
• The ORDER BY clause comes last in the SELECT
statement:
SELECT last_name, job_id, department_id, hire_date
FROM employees
ORDER BY hire_date ;

…


Sorting

• Sorting in descending order:
SELECT last_name, job_id, department_id, hire_date
FROM employees
ORDER BY hire_date DESC ; 1
• Sorting by column alias:
SELECT employee_id, last_name, salary*12 annsal
FROM employees 2
ORDER BY annsal ;

• Sorting by multiple columns:
SELECT last_name, department_id, salary
FROM employees 3
ORDER BY department_id, salary DESC;


Substitution Variables

... salary = ? …
… department_id = ? …
... last_name = ? ...

I want
to query
different
values.


Substitution Variables

• Use iSQL*Plus substitution variables to:
– Temporarily store values with single-ampersand (&)
and double-ampersand (&&) substitution
• Use substitution variables to supplement the
following:
– WHERE conditions
– ORDER BY clauses
– Column expressions
– Table names
– Entire SELECT statements


Using the & Substitution Variable

Use a variable prefixed with an ampersand (&) to
prompt the user for a value:
SELECT employee_id, last_name, salary, department_id
FROM employees
WHERE employee_id = &employee_num ;


Using the & Substitution Variable

101

1
2


Character and Date Values
with Substitution Variables

Use single quotation marks for date and character
values:

SELECT last_name, department_id, salary*12
FROM employees
WHERE job_id = '&job_title' ;


Specifying Column Names,
Expressions, and Text

SELECT employee_id, last_name, job_id,&column_name
FROM employees
WHERE &condition
ORDER BY &order_column ;

salary

salary > 15000

last_name


Using the && Substitution Variable

Use the double ampersand (&&) if you want to reuse
the variable value without prompting the user each
time:
SELECT employee_id, last_name, job_id, &&column_name
FROM employees
ORDER BY &column_name ;

…


Using the iSQL*Plus DEFINE Command

• Use the iSQL*Plus DEFINE command to create and
assign a value to a variable.
• Use the iSQL*Plus UNDEFINE command to remove
a variable.

DEFINE employee_num = 200

FROM employees
WHERE employee_id = &employee_num ;

UNDEFINE employee_num


Using the VERIFY Command

Use the VERIFY command to toggle the display of the
substitution variable, both before and after iSQL*Plus
replaces substitution variables with values:

SET VERIFY ON
FROM employees
WHERE employee_id = &employee_num;

old 3: WHERE employee_id = &employee_num
new 3: WHERE employee_id = 200


Summary

• Use the WHERE clause to restrict rows of output:
– Use the comparison conditions
– Use the BETWEEN, IN, LIKE, and NULL conditions
– Apply the logical AND, OR, and NOT operators
• Use the ORDER BY clause to sort rows of output:
FROM table
[WHERE condition(s)]
[ORDER BY {column, expr, alias} [ASC|DESC]] ;

• Use ampersand substitution in iSQL*Plus to
restrict and sort output at run time



• Selecting data and changing the order of
the rows that are displayed
• Restricting rows by using the WHERE clause
• Sorting rows by using the ORDER BY clause
• Using substitution variables to add flexibility to
your SQL SELECT statements


Using Single-Row Functions to
Customize Output


Objectives

the following:
• Describe various types of functions that are
available in SQL
• Use character, number, and date functions in
SELECT statements
• Describe the use of conversion functions


SQL Functions

Input Output

Function

arg 1 Function performs
action
arg 2
Result
value

arg n


Two Types of SQL Functions

Functions

Single-row Multiple-row
functions functions

Return one result Return one result
per row per set of rows


Single-Row Functions

Single-row functions:
• Manipulate data items
• Accept arguments and return one value
• Act on each row that is returned
• Return one result per row
• May modify the data type
• Can be nested
• Accept arguments that can be a column or an
expression

function_name [(arg1, arg2,...)]


Single-Row Functions

Character

Single-row
General Number
functions

Conversion Date


Character Functions

Character
functions

Case-manipulation Character-manipulation
functions functions

LOWER CONCAT
UPPER SUBSTR
INITCAP LENGTH
INSTR
LPAD | RPAD
TRIM
REPLACE


Case-Manipulation Functions

These functions convert case for character strings:
Function Result
LOWER('SQL Course') sql course
UPPER('SQL Course') SQL COURSE
INITCAP('SQL Course') Sql Course


Using Case-Manipulation Functions

Display the employee number, name, and department
number for employee Higgins:
SELECT employee_id, last_name, department_id
FROM employees
WHERE last_name = 'higgins';
no rows selected

SELECT employee_id, last_name, department_id
FROM employees
WHERE LOWER(last_name) = 'higgins';


Character-Manipulation Functions

These functions manipulate character strings:
Function Result
CONCAT('Hello', 'World') HelloWorld
SUBSTR('HelloWorld',1,5) Hello
LENGTH('HelloWorld') 10
INSTR('HelloWorld', 'W') 6
LPAD(salary,10,'*') *****24000
RPAD(salary, 10, '*') 24000*****
REPLACE BLACK and BLUE
('JACK and JUE','J','BL')
TRIM('H' FROM 'HelloWorld') elloWorld


Using the Character-Manipulation
Functions

1
SELECT employee_id, CONCAT(first_name, last_name) NAME,
job_id, LENGTH (last_name), 2
INSTR(last_name, 'a') "Contains 'a'?"
FROM employees 3
WHERE SUBSTR(job_id, 4) = 'REP';

1 2 3


Number Functions

• ROUND: Rounds value to specified decimal
• TRUNC: Truncates value to specified decimal
• MOD: Returns remainder of division
Function Result
ROUND(45.926, 2) 45.93
TRUNC(45.926, 2) 45.92
MOD(1600, 300) 100


Using the ROUND Function

1 2
SELECT ROUND(45.923,2), ROUND(45.923,0),
ROUND(45.923,-1) 3
FROM DUAL;

1 2 3
DUAL is a dummy table that you can use to view results
from functions and calculations.


Using the TRUNC Function

1 2
SELECT ROUND(45.923,2), ROUND(45.923),
ROUND(45.923,-1) 3
FROM DUAL;

1 2 3


Using the MOD Function

For all employees with job title of Sales Representative,
calculate the remainder of the salary after it is divided
by 5,000.
SELECT last_name, salary, MOD(salary, 5000)
FROM employees
WHERE job_id = 'SA_REP';


Working with Dates

• The Oracle database stores dates in an internal numeric
format: century, year, month, day, hours, minutes, and
seconds.
• The default date display format is DD-MON-RR.
– Enables you to store 21st-century dates in the
20th century by specifying only the last two digits
of the year
– Enables you to store 20th-century dates in the
21st century in the same way
SELECT last_name, hire_date
FROM employees
WHERE hire_date < '01-FEB-88';


Working with Dates

SYSDATE is a function that returns:
• Date
• Time


Arithmetic with Dates

• Add or subtract a number to or from a date for a
resultant date value.
• Subtract two dates to find the number of days
between those dates.
• Add hours to a date by dividing the number of
hours by 24.


Using Arithmetic Operators
with Dates

SELECT last_name, (SYSDATE-hire_date)/7 AS WEEKS
FROM employees
WHERE department_id = 90;


Date Functions

Function Result
MONTHS_BETWEEN Number of months between two dates
ADD_MONTHS Add calendar months to date
NEXT_DAY Next day of the date specified
LAST_DAY Last day of the month
ROUND Round date
TRUNC Truncate date


Using Date Functions

Function Result
MONTHS_BETWEEN 19.6774194
('01-SEP-95','11-JAN-94')
ADD_MONTHS ('11-JAN-94',6) '11-JUL-94'
NEXT_DAY ('01-SEP-95','FRIDAY') '08-SEP-95'
LAST_DAY ('01-FEB-95') '28-FEB-95'


Using Date Functions

Assume SYSDATE = '25-JUL-03':
Function Result
ROUND(SYSDATE,'MONTH') 01-AUG-03
ROUND(SYSDATE ,'YEAR') 01-JAN-04
TRUNC(SYSDATE ,'MONTH') 01-JUL-03
TRUNC(SYSDATE ,'YEAR') 01-JAN-03


Practice 3: Overview of Part 1

• Writing a query that displays the current date
• Creating queries that require the use of numeric,
character, and date functions
• Performing calculations of years and months of
service for an employee


Conversion Functions

Data type
conversion

Implicit data type Explicit data type
conversion conversion


Implicit Data Type Conversion

For assignments, the Oracle server can automatically
convert the following:

From To
VARCHAR2 or CHAR NUMBER
VARCHAR2 or CHAR DATE
NUMBER VARCHAR2
DATE VARCHAR2


Implicit Data Type Conversion

For expression evaluation, the Oracle Server can
automatically convert the following:

From To
VARCHAR2 or CHAR NUMBER
VARCHAR2 or CHAR DATE


Explicit Data Type Conversion

TO_NUMBER TO_DATE

NUMBER CHARACTER DATE

TO_CHAR TO_CHAR


Using the TO_CHAR Function with Dates

TO_CHAR(date, 'format_model')

The format model:
• Must be enclosed by single quotation marks
• Is case-sensitive
• Can include any valid date format element
• Has an fm element to remove padded blanks or
suppress leading zeros
• Is separated from the date value by a comma


Elements of the Date Format Model

Element Result
YYYY Full year in numbers
YEAR Year spelled out (in English)
MM Two-digit value for month
MONTH Full name of the month
MON Three-letter abbreviation of the month
DY Three-letter abbreviation of the day of the
week
DAY Full name of the day of the week
DD Numeric day of the month


Elements of the Date Format Model

• Time elements format the time portion of the date:
HH24:MI:SS AM 15:45:32 PM

• Add character strings by enclosing them in double
quotation marks:
DD "of" MONTH 12 of OCTOBER

• Number suffixes spell out numbers:
ddspth fourteenth


Using the TO_CHAR Function with Dates

SELECT last_name,
TO_CHAR(hire_date, 'fmDD Month YYYY')
AS HIREDATE
FROM employees;

…


Using the TO_CHAR Function with Numbers

TO_CHAR(number, 'format_model')
These are some of the format elements that you can
use with the TO_CHAR function to display a number
value as a character:
Element Result
9 Represents a number
0 Forces a zero to be displayed
$ Places a floating dollar sign
L Uses the floating local currency symbol
. Prints a decimal point
, Prints a comma as thousands indicator


Using the TO_CHAR Function with Numbers

SELECT TO_CHAR(salary, '$99,999.00') SALARY
FROM employees
WHERE last_name = 'Ernst';


Using the TO_NUMBER and TO_DATE
Functions

• Convert a character string to a number format
using the TO_NUMBER function:

TO_NUMBER(char[, 'format_model'])

• Convert a character string to a date format using
the TO_DATE function:

TO_DATE(char[, 'format_model'])

• These functions have an fx modifier. This
modifier specifies the exact matching for the
character argument and date format model of a
TO_DATE function.


RR Date Format

Current Year Specified Date RR Format YY Format
1995 27-OCT-95 1995 1995
1995 27-OCT-17 2017 1917
2001 27-OCT-17 2017 2017
2001 27-OCT-95 1995 2095

If the specified two-digit year is:

0–49 50–99
If two digits The return date is in The return date is in
of the 0–49 the current century the century before
current the current one
year are: The return date is in The return date is in
50–99 the century after the current century
the current one


Example of RR Date Format

To find employees hired prior to 1990, use the RR date
format, which produces the same results whether the
command is run in 1999 or now:
SELECT last_name, TO_CHAR(hire_date, 'DD-Mon-YYYY')
FROM employees
WHERE hire_date < TO_DATE('01-Jan-90','DD-Mon-RR');


Nesting Functions

• Single-row functions can be nested to any level.
• Nested functions are evaluated from deepest level
to the least deep level.

F3(F2(F1(col,arg1),arg2),arg3)

Step 1 = Result 1
Step 2 = Result 2
Step 3 = Result 3


Nesting Functions

SELECT last_name,
UPPER(CONCAT(SUBSTR (LAST_NAME, 1, 8), '_US'))
FROM employees


General Functions

The following functions work with any data type and
pertain to using nulls:
• NVL (expr1, expr2)
• NVL2 (expr1, expr2, expr3)
• NULLIF (expr1, expr2)
• COALESCE (expr1, expr2, ..., exprn)


NVL Function

Converts a null value to an actual value:
• Data types that can be used are date, character,
and number.
• Data types must match:
– NVL(commission_pct,0)
– NVL(hire_date,'01-JAN-97')
– NVL(job_id,'No Job Yet')


Using the NVL Function

SELECT last_name, salary, NVL(commission_pct, 0), 1
(salary*12) + (salary*12*NVL(commission_pct, 0)) AN_SAL
FROM employees;
2

…

1 2


Using the NVL2 Function

SELECT last_name, salary, commission_pct, 1
NVL2(commission_pct,
'SAL+COMM', 'SAL') income 2
FROM employees WHERE department_id IN (50, 80);

1 2


Using the NULLIF Function
1
SELECT first_name, LENGTH(first_name) "expr1",
last_name, LENGTH(last_name) "expr2", 2
NULLIF(LENGTH(first_name), LENGTH(last_name)) result 3
FROM employees;

…
1 2 3


Using the COALESCE Function

• The advantage of the COALESCE function over the
NVL function is that the COALESCE function can
take multiple alternate values.
• If the first expression is not null, the COALESCE
function returns that expression; otherwise, it
does a COALESCE of the remaining expressions.


Using the COALESCE Function

SELECT last_name,
COALESCE(manager_id,commission_pct, -1) comm
FROM employees
ORDER BY commission_pct;

…


Conditional Expressions

• Provide the use of IF-THEN-ELSE logic within a
SQL statement
• Use two methods:
– CASE expression
– DECODE function


CASE Expression

Facilitates conditional inquiries by doing the work of
an IF-THEN-ELSE statement:

CASE expr WHEN comparison_expr1 THEN return_expr1
[WHEN comparison_expr2 THEN return_expr2
WHEN comparison_exprn THEN return_exprn
ELSE else_expr]
END


Using the CASE Expression

Facilitates conditional inquiries by doing the work of
an IF-THEN-ELSE statement:
SELECT last_name, job_id, salary,
CASE job_id WHEN 'IT_PROG' THEN 1.10*salary
WHEN 'ST_CLERK' THEN 1.15*salary
WHEN 'SA_REP' THEN 1.20*salary
ELSE salary END "REVISED_SALARY"
FROM employees;

…

…


DECODE Function

Facilitates conditional inquiries by doing the work of a
CASE expression or an IF-THEN-ELSE statement:

DECODE(col|expression, search1, result1
[, search2, result2,...,]
[, default])


Using the DECODE Function

SELECT last_name, job_id, salary,
DECODE(job_id, 'IT_PROG', 1.10*salary,
'ST_CLERK', 1.15*salary,
'SA_REP', 1.20*salary,
salary)
REVISED_SALARY
FROM employees;

…

…


Using the DECODE Function

Display the applicable tax rate for each employee in
department 80:
SELECT last_name, salary,
DECODE (TRUNC(salary/2000, 0),
0, 0.00,
1, 0.09,
2, 0.20,
3, 0.30,
4, 0.40,
5, 0.42,
6, 0.44,
0.45) TAX_RATE
FROM employees


Summary

• Perform calculations on data using functions
• Modify individual data items using functions
• Manipulate output for groups of rows using
functions
• Alter date formats for display using functions
• Convert column data types using functions
• Use NVL functions
• Use IF-THEN-ELSE logic



• Creating queries that require the use of numeric,
character, and date functions
• Using concatenation with functions
• Writing case-insensitive queries to test the
usefulness of character functions
• Performing calculations of years and months of
service for an employee
• Determining the review date for an employee


Reporting Aggregated Data
Using the Group Functions


Objectives

the following:
• Identify the available group functions
• Describe the use of group functions
• Group data by using the GROUP BY clause
• Include or exclude grouped rows by using the
HAVING clause


What Are Group Functions?

Group functions operate on sets of rows to give one
result per group.
EMPLOYEES

Maximum salary in
EMPLOYEES table

…


Types of Group Functions

• AVG
• COUNT
• MAX
Group
• MIN functions
• STDDEV
• SUM
• VARIANCE


Group Functions: Syntax

SELECT [column,] group_function(column), ...
FROM table
[WHERE condition]
[GROUP BY column]
[ORDER BY column];


Using the AVG and SUM Functions

You can use AVG and SUM for numeric data.
SELECT AVG(salary), MAX(salary),
MIN(salary), SUM(salary)
FROM employees
WHERE job_id LIKE '%REP%';


Using the MIN and MAX Functions

You can use MIN and MAX for numeric, character, and
date data types.
SELECT MIN(hire_date), MAX(hire_date)
FROM employees;


Using the COUNT Function

COUNT(*) returns the number of rows in a table:
SELECT COUNT(*)
1 FROM employees

COUNT(expr) returns the number of rows with non-
null values for the expr:
SELECT COUNT(commission_pct)
2 FROM employees


Using the DISTINCT Keyword

• COUNT(DISTINCT expr) returns the number of
distinct non-null values of the expr.
• To display the number of distinct department
values in the EMPLOYEES table:
SELECT COUNT(DISTINCT department_id)
FROM employees;


Group Functions and Null Values

Group functions ignore null values in the column:
SELECT AVG(commission_pct)
1 FROM employees;

The NVL function forces group functions to include
null values:
SELECT AVG(NVL(commission_pct, 0))
2 FROM employees;


Creating Groups of Data

EMPLOYEES
4400

9500

3500 Average
salary in
EMPLOYEES
6400 table for each
department
10033

…


Creating Groups of Data:
GROUP BY Clause Syntax

SELECT column, group_function(column)
FROM table
[WHERE condition]
[GROUP BY group_by_expression]
[ORDER BY column];

You can divide rows in a table into smaller groups by
using the GROUP BY clause.


Using the GROUP BY Clause

All columns in the SELECT list that are not in group
functions must be in the GROUP BY clause.

SELECT department_id, AVG(salary)
FROM employees
GROUP BY department_id ;



The GROUP BY column does not have to be in the
SELECT list.
SELECT AVG(salary)
FROM employees
GROUP BY department_id ;


Grouping by More Than One Column

EMPLOYEES

Add the
salaries in
the EMPLOYEES
table for
each job,
grouped by
department
…


on Multiple Columns

SELECT department_id dept_id, job_id, SUM(salary)
FROM employees
GROUP BY department_id, job_id ;


Illegal Queries
Using Group Functions

Any column or expression in the SELECT list that is not
an aggregate function must be in the GROUP BY clause:
SELECT department_id, COUNT(last_name)
FROM employees;

SELECT department_id, COUNT(last_name)
*
ERROR at line 1:
ORA-00937: not a single-group group function

Column missing in the GROUP BY clause


Illegal Queries
Using Group Functions

• You cannot use the WHERE clause to restrict groups.
• You use the HAVING clause to restrict groups.
• You cannot use group functions in the WHERE clause.
SELECT department_id, AVG(salary)
FROM employees
WHERE AVG(salary) > 8000
GROUP BY department_id;

WHERE AVG(salary) > 8000
*
ERROR at line 3:
ORA-00934: group function is not allowed here
Cannot use the WHERE clause to restrict groups


Restricting Group Results

EMPLOYEES

The maximum
salary
per department
when it is
greater than
$10,000
…


Restricting Group Results
with the HAVING Clause

When you use the HAVING clause, the Oracle server
restricts groups as follows:
1. Rows are grouped.
2. The group function is applied.
3. Groups matching the HAVING clause are
displayed.
SELECT column, group_function
FROM table
[WHERE condition]
[HAVING group_condition]
[ORDER BY column];


Using the HAVING Clause

SELECT department_id, MAX(salary)
FROM employees
GROUP BY department_id
HAVING MAX(salary)>10000 ;


Using the HAVING Clause

SELECT job_id, SUM(salary) PAYROLL
FROM employees
WHERE job_id NOT LIKE '%REP%'
GROUP BY job_id
HAVING SUM(salary) > 13000
ORDER BY SUM(salary);


Nesting Group Functions

Display the maximum average salary:
SELECT MAX(AVG(salary))
FROM employees
GROUP BY department_id;


Summary

• Use the group functions COUNT, MAX, MIN, and AVG
• Write queries that use the GROUP BY clause
• Write queries that use the HAVING clause

SELECT column, group_function
FROM table
[WHERE condition]
[HAVING group_condition]
[ORDER BY column];



• Writing queries that use the group functions
• Grouping by rows to achieve more than one result
• Restricting groups by using the HAVING clause


Displaying Data
from Multiple Tables


Objectives

the following:
• Write SELECT statements to access data from
more than one table using equijoins and non-
equijoins
• Join a table to itself by using a self-join
• View data that generally does not meet a join
condition by using outer joins
• Generate a Cartesian product of all rows from two
or more tables


Obtaining Data from Multiple Tables

EMPLOYEES DEPARTMENTS

…

…


Types of Joins

Joins that are compliant with the SQL:1999 standard
include the following:
• Cross joins
• Natural joins
• USING clause
• Full (or two-sided) outer joins
• Arbitrary join conditions for outer joins


Joining Tables Using SQL:1999 Syntax

Use a join to query data from more than one table:
SELECT table1.column, table2.column
FROM table1
[NATURAL JOIN table2] |
[JOIN table2 USING (column_name)] |
[JOIN table2
ON (table1.column_name = table2.column_name)]|
[LEFT|RIGHT|FULL OUTER JOIN table2
ON (table1.column_name = table2.column_name)]|
[CROSS JOIN table2];


Creating Natural Joins

• The NATURAL JOIN clause is based on all columns
in the two tables that have the same name.
• It selects rows from the two tables that have equal
values in all matched columns.
• If the columns having the same names have
different data types, an error is returned.


Retrieving Records with Natural Joins

SELECT department_id, department_name,
location_id, city
FROM departments
NATURAL JOIN locations ;


Creating Joins with the USING Clause

• If several columns have the same names but the
data types do not match, the NATURAL JOIN clause
can be modified with the USING clause to specify
the columns that should be used for an equijoin.
• Use the USING clause to match only one column
when more than one column matches.
• Do not use a table name or alias in the referenced
columns.
• The NATURAL JOIN and USING clauses are
mutually exclusive.


Joining Column Names


… …
Foreign key Primary key


Retrieving Records with the USING Clause

SELECT employees.employee_id, employees.last_name,
departments.location_id, department_id
FROM employees JOIN departments
USING (department_id) ;

…


Qualifying Ambiguous
Column Names

• Use table prefixes to qualify column names that
are in multiple tables.
• Use table prefixes to improve performance.
• Use column aliases to distinguish columns that
have identical names but reside in different tables.
• Do not use aliases on columns that are identified
in the USING clause and listed elsewhere in the
SQL statement.


Using Table Aliases

• Use table aliases to simplify queries.
• Use table aliases to improve performance.
SELECT e.employee_id, e.last_name,
d.location_id, department_id
FROM employees e JOIN departments d
USING (department_id) ;


Creating Joins with the ON Clause

• The join condition for the natural join is basically
an equijoin of all columns with the same name.
• Use the ON clause to specify arbitrary conditions
or specify columns to join.
• The join condition is separated from other search
conditions.
• The ON clause makes code easy to understand.


Retrieving Records with the ON Clause

SELECT e.employee_id, e.last_name, e.department_id,
d.department_id, d.location_id
ON (e.department_id = d.department_id);

…


Self-Joins Using the ON Clause

EMPLOYEES (WORKER) EMPLOYEES (MANAGER)

… …

MANAGER_ID in the WORKER table is equal to
EMPLOYEE_ID in the MANAGER table.


Self-Joins Using the ON Clause

SELECT e.last_name emp, m.last_name mgr
FROM employees e JOIN employees m
ON (e.manager_id = m.employee_id);

…


Applying Additional Conditions
to a Join

ON (e.department_id = d.department_id)
AND e.manager_id = 149 ;


Creating Three-Way Joins with the
ON Clause

SELECT employee_id, city, department_name
FROM employees e
JOIN departments d
ON d.department_id = e.department_id
JOIN locations l
ON d.location_id = l.location_id;

…


Non-Equijoins

EMPLOYEES JOB_GRADES

Salary in the EMPLOYEES
table must be between
… lowest salary and highest
salary in the JOB_GRADES
table.


Retrieving Records
with Non-Equijoins

SELECT e.last_name, e.salary, j.grade_level
FROM employees e JOIN job_grades j
ON e.salary
BETWEEN j.lowest_sal AND j.highest_sal;

…


Outer Joins

DEPARTMENTS EMPLOYEES

…

There are no employees in
department 190.


INNER Versus OUTER Joins

• In SQL:1999, the join of two tables returning only
matched rows is called an inner join.
• A join between two tables that returns the results
of the inner join as well as the unmatched rows
from the left (or right) tables is called a left (or
right) outer join.
• A join between two tables that returns the results
of an inner join as well as the results of a left and
right join is a full outer join.


LEFT OUTER JOIN

SELECT e.last_name, e.department_id, d.department_name
FROM employees e LEFT OUTER JOIN departments d
ON (e.department_id = d.department_id) ;

…


RIGHT OUTER JOIN

FROM employees e RIGHT OUTER JOIN departments d

…


FULL OUTER JOIN

SELECT e.last_name, d.department_id, d.department_name
FROM employees e FULL OUTER JOIN departments d

…


Cartesian Products

• A Cartesian product is formed when:
– A join condition is omitted
– A join condition is invalid
– All rows in the first table are joined to all rows in the
second table
• To avoid a Cartesian product, always include a
valid join condition.


Generating a Cartesian Product

EMPLOYEES (20 rows) DEPARTMENTS (8 rows)

…

Cartesian product:
20 x 8 = 160 rows

…


Creating Cross Joins

• The CROSS JOIN clause produces the cross-
product of two tables.
• This is also called a Cartesian product between
the two tables.

SELECT last_name, department_name
FROM employees
CROSS JOIN departments ;

…


Summary

In this lesson, you should have learned how to use
joins to display data from multiple tables by using:
• Equijoins
• Non-equijoins
• Outer joins
• Self-joins
• Cross joins
• Natural joins
• Full (or two-sided) outer joins



• Joining tables using an equijoin
• Performing outer and self-joins
• Adding conditions


Using Subqueries to Solve Queries


Objectives

the following:
• Define subqueries
• Describe the types of problems that subqueries
can solve
• List the types of subqueries
• Write single-row and multiple-row subqueries


Using a Subquery
to Solve a Problem

Who has a salary greater than Abel’s?

Main query:

Which employees have salaries greater
than Abel’s salary?

Subquery:

What is Abel’s salary?


Subquery Syntax

SELECT select_list
FROM table
WHERE expr operator
(SELECT select_list
FROM table);

• The subquery (inner query) executes once before
the main query (outer query).
• The result of the subquery is used by the main
query.


Using a Subquery

SELECT last_name
FROM employees 11000
WHERE salary >
(SELECT salary
FROM employees
WHERE last_name = 'Abel');


Guidelines for Using Subqueries

• Enclose subqueries in parentheses.
• Place subqueries on the right side of the
comparison condition.
• The ORDER BY clause in the subquery is not
needed unless you are performing Top-N analysis.
• Use single-row operators with single-row
subqueries, and use multiple-row operators with
multiple-row subqueries.


Types of Subqueries

• Single-row subquery
Main query
returns
Subquery ST_CLERK

• Multiple-row subquery
Main query
returns ST_CLERK
Subquery
SA_MAN


Single-Row Subqueries

• Return only one row
• Use single-row comparison operators
Operator Meaning
= Equal to
> Greater than
>= Greater than or equal to
< Less than
<= Less than or equal to
<> Not equal to


Executing Single-Row Subqueries

FROM employees
WHERE job_id = ST_CLERK
(SELECT job_id
FROM employees
WHERE employee_id = 141)
AND salary > 2600
(SELECT salary
FROM employees
WHERE employee_id = 143);


Using Group Functions in a Subquery

FROM employees 2500
WHERE salary =
(SELECT MIN(salary)
FROM employees);


The HAVING Clause with Subqueries

• The Oracle server executes subqueries first.
• The Oracle server returns results into the HAVING
clause of the main query.
SELECT department_id, MIN(salary)
FROM employees
GROUP BY department_id 2500
HAVING MIN(salary) >
(SELECT MIN(salary)
FROM employees
WHERE department_id = 50);


What Is Wrong with This Statement?

SELECT employee_id, last_name
FROM employees
WHERE salary =
(SELECT MIN(salary)
FROM employees
GROUP BY department_id);

ERROR at line 4:
ORA-01427: single-row subquery returns more than
one row

Single-row operator with multiple-row subquery


Will This Statement Return Rows?

SELECT last_name, job_id
FROM employees
WHERE job_id =
(SELECT job_id
FROM employees
WHERE last_name = 'Haas');

no rows selected

Subquery returns no values.


Multiple-Row Subqueries

• Return more than one row
• Use multiple-row comparison operators

Operator Meaning
IN Equal to any member in the list
ANY Compare value to each value returned by the
subquery
ALL Compare value to every value returned by
the subquery


Using the ANY Operator
in Multiple-Row Subqueries

FROM employees 9000, 6000, 4200
WHERE salary < ANY
(SELECT salary
FROM employees
WHERE job_id = 'IT_PROG')
AND job_id <> 'IT_PROG';

…


Using the ALL Operator
in Multiple-Row Subqueries

FROM employees 9000, 6000, 4200
WHERE salary < ALL
(SELECT salary
FROM employees
WHERE job_id = 'IT_PROG')
AND job_id <> 'IT_PROG';


Null Values in a Subquery

SELECT emp.last_name
FROM employees emp
WHERE emp.employee_id NOT IN
(SELECT mgr.manager_id
FROM employees mgr);

no rows selected


Summary

• Identify when a subquery can help solve a
question
• Write subqueries when a query is based on
unknown values
SELECT select_list
FROM table
WHERE expr operator
(SELECT select_list
FROM table);



• Creating subqueries to query values based on
unknown criteria
• Using subqueries to find out which values exist in
one set of data and not in another


Using the Set Operators


Objectives

the following:
• Describe set operators
• Use a set operator to combine multiple queries
into a single query
• Control the order of rows returned


Set Operators
A B A B

UNION/UNION ALL

A B

INTERSECT

A B

MINUS


Tables Used in This Lesson

The tables used in this lesson are:
• EMPLOYEES: Provides details regarding all
current employees
• JOB_HISTORY: Records the details of the start
date and end date of the former job, and the job
identification number and department when an
employee switches jobs


UNION Operator

A B

The UNION operator returns results from both
queries after eliminating duplications.


Using the UNION Operator

Display the current and previous job details of all
employees. Display each employee only once.
SELECT employee_id, job_id
FROM employees
UNION
FROM job_history;

…
…


UNION ALL Operator

A B

The UNION ALL operator returns results from both
queries, including all duplications.


Using the UNION ALL Operator

Display the current and previous departments of all
employees.
SELECT employee_id, job_id, department_id
FROM employees
UNION ALL
SELECT employee_id, job_id, department_id
FROM job_history
ORDER BY employee_id;

…

…


INTERSECT Operator

A B

The INTERSECT operator returns rows that are
common to both queries.


Using the INTERSECT Operator

Display the employee IDs and job IDs of those
employees who currently have a job title that is the
same as their job title when they were initially hired
(that is, they changed jobs but have now gone back to
doing their original job).
FROM employees
INTERSECT
FROM job_history;


MINUS Operator

A B

The MINUS operator returns rows in the first query
that are not present in the second query.


MINUS Operator

Display the employee IDs of those employees who
have not changed their jobs even once.
SELECT employee_id,job_id
FROM employees
MINUS
SELECT employee_id,job_id
FROM job_history;

…


Set Operator Guidelines

• The expressions in the SELECT lists must match in
number and data type.
• Parentheses can be used to alter the sequence of
execution.
• The ORDER BY clause:
– Can appear only at the very end of the statement
– Will accept the column name, aliases from the first
SELECT statement, or the positional notation


The Oracle Server and Set Operators

• Duplicate rows are automatically eliminated
except in UNION ALL.
• Column names from the first query appear in the
result.
• The output is sorted in ascending order by default
except in UNION ALL.


Matching the SELECT Statements

Using the UNION operator, display the department ID,
location, and hire date for all employees.
SELECT department_id, TO_NUMBER(null)
location, hire_date
FROM employees
UNION
SELECT department_id, location_id, TO_DATE(null)
FROM departments;

…


Matching the SELECT Statement:
Example

Using the UNION operator, display the employee ID, job
ID, and salary of all employees.

SELECT employee_id, job_id,salary
FROM employees
UNION
SELECT employee_id, job_id,0
FROM job_history;

…


Controlling the Order of Rows

Produce an English sentence using two UNION
operators.
COLUMN a_dummy NOPRINT
SELECT 'sing' AS "My dream", 3 a_dummy
FROM dual
UNION
SELECT 'I''d like to teach', 1 a_dummy
FROM dual
UNION
SELECT 'the world to', 2 a_dummy
FROM dual
ORDER BY a_dummy;


Summary

• Use UNION to return all distinct rows
• Use UNION ALL to return all rows, including
duplicates
• Use INTERSECT to return all rows that are shared
by both queries
• Use MINUS to return all distinct rows that are
selected by the first query but not by the second
• Use ORDER BY only at the very end of the
statement



In this practice, you use the set operators to create
reports:
• Using the UNION operator
• Using the INTERSECTION operator
• Using the MINUS operator


Manipulating Data


Objectives

the following:
• Describe each data manipulation language (DML)
statement
• Insert rows into a table
• Update rows in a table
• Delete rows from a table
• Control transactions


Data Manipulation Language

• A DML statement is executed when you:
– Add new rows to a table
– Modify existing rows in a table
– Remove existing rows from a table
• A transaction consists of a collection of DML
statements that form a logical unit of work.


Adding a New Row to a Table
New
DEPARTMENTS row

Insert new row
into the
DEPARTMENTS table


INSERT Statement Syntax

• Add new rows to a table by using the INSERT
statement:
INSERT INTO table [(column [, column...])]
VALUES (value [, value...]);

• With this syntax, only one row is inserted at a
time.


Inserting New Rows

• Insert a new row containing values for each
column.
• List values in the default order of the columns in
the table.
• Optionally, list the columns in the INSERT clause.
INSERT INTO departments(department_id,
department_name, manager_id, location_id)
VALUES (70, 'Public Relations', 100, 1700);
1 row created.

• Enclose character and date values in single
quotation marks.


Inserting Rows with Null Values

• Implicit method: Omit the column from the
column list.

INSERT INTO departments (department_id,
department_name )
VALUES (30, 'Purchasing');
1 row created.

• Explicit method: Specify the NULL keyword in the
VALUES clause.
INSERT INTO departments
VALUES (100, 'Finance', NULL, NULL);
1 row created.


Inserting Special Values

The SYSDATE function records the current date and
time.
INSERT INTO employees (employee_id,
first_name, last_name,
email, phone_number,
hire_date, job_id, salary,
commission_pct, manager_id,
department_id)
VALUES (113,
'Louis', 'Popp',
'LPOPP', '515.124.4567',
SYSDATE, 'AC_ACCOUNT', 6900,
NULL, 205, 100);
1 row created.


Inserting Specific Date Values

• Add a new employee.
INSERT INTO employees
VALUES (114,
'Den', 'Raphealy',
'DRAPHEAL', '515.127.4561',
TO_DATE('FEB 3, 1999', 'MON DD, YYYY'),
'AC_ACCOUNT', 11000, NULL, 100, 30);
1 row created.

• Verify your addition.


Creating a Script

• Use & substitution in a SQL statement to prompt
for values.
• & is a placeholder for the variable value.
(department_id, department_name, location_id)
VALUES (&department_id, '&department_name',&location);

1 row created.


Copying Rows
from Another Table

• Write your INSERT statement with a subquery:
INSERT INTO sales_reps(id, name, salary, commission_pct)
SELECT employee_id, last_name, salary, commission_pct
FROM employees
WHERE job_id LIKE '%REP%';

4 rows created.

• Do not use the VALUES clause.
• Match the number of columns in the INSERT
clause to those in the subquery.


Changing Data in a Table

EMPLOYEES

Update rows in the EMPLOYEES table:


UPDATE Statement Syntax

• Modify existing rows with the UPDATE statement:
UPDATE table
SET column = value [, column = value, ...]
[WHERE condition];

• Update more than one row at a time (if required).


Updating Rows in a Table

• Specific row or rows are modified if you specify
the WHERE clause:
UPDATE employees
SET department_id = 70
WHERE employee_id = 113;
1 row updated.

• All rows in the table are modified if you omit the
WHERE clause:
UPDATE copy_emp
SET department_id = 110;
22 rows updated.


Updating Two Columns with a Subquery

Update employee 114’s job and salary to match that of
employee 205.
UPDATE employees
SET job_id = (SELECT job_id
FROM employees
WHERE employee_id = 205),
salary = (SELECT salary
FROM employees
1 row updated.


Updating Rows Based
on Another Table

Use subqueries in UPDATE statements to update
rows in a table based on values from another table:
UPDATE copy_emp
SET department_id = (SELECT department_id
FROM employees
WHERE job_id = (SELECT job_id
FROM employees
WHERE employee_id = 200);
1 row updated.


Removing a Row from a Table

DEPARTMENTS

Delete a row from the DEPARTMENTS table:


DELETE Statement

You can remove existing rows from a table by using
the DELETE statement:

DELETE [FROM] table
[WHERE condition];


Deleting Rows from a Table

• Specific rows are deleted if you specify the WHERE
clause:
DELETE FROM departments
WHERE department_name = 'Finance';
1 row deleted.

• All rows in the table are deleted if you omit the
WHERE clause:
DELETE FROM copy_emp;
22 rows deleted.


Deleting Rows Based
on Another Table

Use subqueries in DELETE statements to remove rows
from a table based on values from another table:
DELETE FROM employees
WHERE department_id =
(SELECT department_id
FROM departments
WHERE department_name
LIKE '%Public%');
1 row deleted.


TRUNCATE Statement

• Removes all rows from a table, leaving the table
empty and the table structure intact
• Is a data definition language (DDL) statement
rather than a DML statement; cannot easily be
undone
• Syntax:
TRUNCATE TABLE table_name;

• Example:
TRUNCATE TABLE copy_emp;


Using a Subquery in an INSERT Statement

INSERT INTO
(SELECT employee_id, last_name,
email, hire_date, job_id, salary,
department_id
FROM employees
WHERE department_id = 50)
VALUES (99999, 'Taylor', 'DTAYLOR',
TO_DATE('07-JUN-99', 'DD-MON-RR'),
'ST_CLERK', 5000, 50);

1 row created.


Using a Subquery in an INSERT Statement

Verify the results:
SELECT employee_id, last_name, email, hire_date,
job_id, salary, department_id
FROM employees


Database Transactions

A database transaction consists of one of the
following:
• DML statements that constitute one consistent
change to the data
• One DDL statement
• One data control language (DCL) statement


Database Transactions

• Begin when the first DML SQL statement is
executed.
• End with one of the following events:
– A COMMIT or ROLLBACK statement is issued.
– A DDL or DCL statement executes (automatic
commit).
– The user exits iSQL*Plus.
– The system crashes.


Advantages of COMMIT
and ROLLBACK Statements

With COMMIT and ROLLBACK statements, you can:
• Ensure data consistency
• Preview data changes before making changes
permanent
• Group logically related operations


Controlling Transactions
Time COMMIT

Transaction

DELETE

SAVEPOINT A

INSERT

UPDATE

SAVEPOINT B

INSERT
ROLLBACK ROLLBACK ROLLBACK
to SAVEPOINT B to SAVEPOINT A


Rolling Back Changes to a Marker

• Create a marker in a current transaction by using
the SAVEPOINT statement.
• Roll back to that marker by using the ROLLBACK
TO SAVEPOINT statement.
UPDATE...
SAVEPOINT update_done;
Savepoint created.
INSERT...
ROLLBACK TO update_done;
Rollback complete.


Implicit Transaction Processing

• An automatic commit occurs under the following
circumstances:
– DDL statement is issued
– DCL statement is issued
– Normal exit from iSQL*Plus, without explicitly
issuing COMMIT or ROLLBACK statements
• An automatic rollback occurs under an abnormal
termination of iSQL*Plus or a system failure.


State of the Data
Before COMMIT or ROLLBACK

• The previous state of the data can be recovered.
• The current user can review the results of the DML
operations by using the SELECT statement.
• Other users cannot view the results of the DML
statements by the current user.
• The affected rows are locked; other users cannot
change the data in the affected rows.


State of the Data After COMMIT

• Data changes are made permanent in the
database.
• The previous state of the data is permanently lost.
• All users can view the results.
• Locks on the affected rows are released; those
rows are available for other users to manipulate.
• All savepoints are erased.


Committing Data

• Make the changes:
DELETE FROM employees
1 row deleted.

VALUES (290, 'Corporate Tax', NULL, 1700);
1 row created.

• Commit the changes:
COMMIT;
Commit complete.


State of the Data After ROLLBACK

Discard all pending changes by using the ROLLBACK
statement:
• Data changes are undone.
• Previous state of the data is restored.
• Locks on the affected rows are released.
DELETE FROM copy_emp;
22 rows deleted.
ROLLBACK ;
Rollback complete.


State of the Data After ROLLBACK

DELETE FROM test;
25,000 rows deleted.

ROLLBACK;
Rollback complete.

DELETE FROM test WHERE id = 100;
1 row deleted.

SELECT * FROM test WHERE id = 100;
No rows selected.

COMMIT;
Commit complete.


Statement-Level Rollback

• If a single DML statement fails during execution,
only that statement is rolled back.
• The Oracle server implements an implicit
savepoint.
• All other changes are retained.
• The user should terminate transactions explicitly
by executing a COMMIT or ROLLBACK statement.


Read Consistency

• Read consistency guarantees a consistent view of
the data at all times.
• Changes made by one user do not conflict with
changes made by another user.
• Read consistency ensures that on the same data:
– Readers do not wait for writers
– Writers do not wait for readers


Implementation of Read Consistency

User A
UPDATE employees Data
SET salary = 7000 blocks
WHERE last_name = 'Grant';

Undo
segments

Changed
SELECT * and
FROM userA.employees; Read- unchanged
consistent data
image Before
change
(“old” data)
User B


Summary

In this lesson, you should have learned how to use the
following statements:
Function Description
INSERT Adds a new row to the table
UPDATE Modifies existing rows in the table
DELETE Removes existing rows from the table
COMMIT Makes all pending changes permanent
SAVEPOINT Is used to roll back to the savepoint marker
ROLLBACK Discards all pending data changes



• Inserting rows into the tables
• Updating and deleting rows in the table
• Controlling transactions


Using DDL Statements
to Create and Manage Tables


Objectives

the following:
• Categorize the main database objects
• Review the table structure
• List the data types that are available for columns
• Create a simple table
• Understand how constraints are created at the
time of table creation
• Describe how schema objects work


Database Objects

Object Description
Table Basic unit of storage; composed of rows
View Logically represents subsets of data from
one or more tables
Sequence Generates numeric values
Index Improves the performance of some
queries
Synonym Gives alternative names to objects


Naming Rules

Table names and column names:
• Must begin with a letter
• Must be 1–30 characters long
• Must contain only A–Z, a–z, 0–9, _, $, and #
• Must not duplicate the name of another object
owned by the same user
• Must not be an Oracle server reserved word


CREATE TABLE Statement

• You must have:
– CREATE TABLE privilege
– A storage area
CREATE TABLE [schema.]table
(column datatype [DEFAULT expr][, ...]);

• You specify:
– Table name
– Column name, column data type, and column size


Referencing Another User’s Tables

• Tables belonging to other users are not in the
user’s schema.
• You should use the owner’s name as a prefix to
those tables.

USERA USERB
SELECT * SELECT *
FROM userB.employees; FROM userA.employees;


DEFAULT Option

• Specify a default value for a column during an
insert.
... hire_date DATE DEFAULT SYSDATE, ...

• Literal values, expressions, or SQL functions are
legal values.
• Another column’s name or a pseudocolumn are
illegal values.
• The default data type must match the column data
type.
CREATE TABLE hire_dates
(id NUMBER(8),
hire_date DATE DEFAULT SYSDATE);
Table created.


Creating Tables

• Create the table.
CREATE TABLE dept
(deptno NUMBER(2),
dname VARCHAR2(14),
loc VARCHAR2(13),
create_date DATE DEFAULT SYSDATE);
Table created.

• Confirm table creation.
DESCRIBE dept


Data Types

Data Type Description
VARCHAR2(size) Variable-length character data
CHAR(size) Fixed-length character data
NUMBER(p,s) Variable-length numeric data
DATE Date and time values
LONG Variable-length character data (up to 2 GB)
CLOB Character data (up to 4 GB)
RAW and LONG Raw binary data
RAW
BLOB Binary data (up to 4 GB)
BFILE Binary data stored in an external file (up to 4 GB)
ROWID A base-64 number system representing the unique
address of a row in its table


Datetime Data Types

You can use several datetime data types:

Data Type Description
TIMESTAMP Date with fractional seconds
INTERVAL YEAR TO Stored as an interval of years
MONTH and months
INTERVAL DAY TO Stored as an interval of days, hours,
SECOND minutes, and seconds


Datetime Data Types

• The TIMESTAMP data type is an extension of the
DATE data type.
• It stores the year, month, and day of the DATE data
type plus hour, minute, and second values as well
as the fractional second value.
• You can optionally specify the time zone.
TIMESTAMP[(fractional_seconds_precision)]

WITH TIME ZONE

WITH LOCAL TIME ZONE


Datetime Data Types

• The INTERVAL YEAR TO MONTH data type stores a
period of time using the YEAR and MONTH datetime
fields:
INTERVAL YEAR [(year_precision)] TO MONTH

• The INTERVAL DAY TO SECOND data type stores a
period of time in terms of days, hours, minutes,
and seconds:
INTERVAL DAY [(day_precision)]
TO SECOND [(fractional_seconds_precision)]


Including Constraints

• Constraints enforce rules at the table level.
• Constraints prevent the deletion of a table if there
are dependencies.
• The following constraint types are valid:
– NOT NULL
– UNIQUE
– PRIMARY KEY
– FOREIGN KEY
– CHECK


Constraint Guidelines

• You can name a constraint, or the Oracle server
generates a name by using the SYS_Cn format.
• Create a constraint at either of the following times:
– At the same time as the table is created
– After the table has been created
• Define a constraint at the column or table level.
• View a constraint in the data dictionary.


Defining Constraints

• Syntax:
CREATE TABLE [schema.]table
(column datatype [DEFAULT expr]
[column_constraint],
...
[table_constraint][,...]);
• Column-level constraint:
column [CONSTRAINT constraint_name] constraint_type,

• Table-level constraint:
column,...
[CONSTRAINT constraint_name] constraint_type
(column, ...),


Defining Constraints

• Column-level constraint:
CREATE TABLE employees(
employee_id NUMBER(6)
CONSTRAINT emp_emp_id_pk PRIMARY KEY, 1
first_name VARCHAR2(20),
...);
• Table-level constraint:
employee_id NUMBER(6),
first_name VARCHAR2(20),
...
job_id VARCHAR2(10) NOT NULL,
2
CONSTRAINT emp_emp_id_pk
PRIMARY KEY (EMPLOYEE_ID));


NOT NULL Constraint

Ensures that null values are not permitted for the
column:

…

NOT NULL constraint NOT NULL Absence of NOT NULL
(No row can contain constraint constraint
a null value for (Any row can contain
this column.) a null value for this
column.)


UNIQUE Constraint

UNIQUE constraint
EMPLOYEES

…
INSERT INTO

Allowed
Not allowed:
already exists


UNIQUE Constraint

Defined at either the table level or the column level:

last_name VARCHAR2(25) NOT NULL,
email VARCHAR2(25),
salary NUMBER(8,2),
commission_pct NUMBER(2,2),
hire_date DATE NOT NULL,
...
CONSTRAINT emp_email_uk UNIQUE(email));


PRIMARY KEY Constraint

DEPARTMENTS
PRIMARY KEY

…
Not allowed INSERT INTO
(null value)

Not allowed
(50 already exists)


FOREIGN KEY Constraint
DEPARTMENTS

PRIMARY
KEY
…

EMPLOYEES
FOREIGN
KEY

… Not allowed
INSERT INTO (9 does not
exist)
Allowed


FOREIGN KEY Constraint

Defined at either the table level or the column level:

last_name VARCHAR2(25) NOT NULL,
email VARCHAR2(25),
salary NUMBER(8,2),
commission_pct NUMBER(2,2),
hire_date DATE NOT NULL,
...
department_id NUMBER(4),
CONSTRAINT emp_dept_fk FOREIGN KEY (department_id)
REFERENCES departments(department_id),
CONSTRAINT emp_email_uk UNIQUE(email));


FOREIGN KEY Constraint:
Keywords

• FOREIGN KEY: Defines the column in the child
table at the table-constraint level
• REFERENCES: Identifies the table and column
in the parent table
• ON DELETE CASCADE: Deletes the dependent
rows in the child table when a row in the
parent table is deleted
• ON DELETE SET NULL: Converts dependent
foreign key values to null


CHECK Constraint

• Defines a condition that each row must satisfy
• The following expressions are not allowed:
– References to CURRVAL, NEXTVAL, LEVEL, and
ROWNUM pseudocolumns
– Calls to SYSDATE, UID, USER, and USERENV
functions
– Queries that refer to other values in other rows
..., salary NUMBER(2)
CONSTRAINT emp_salary_min
CHECK (salary > 0),...


CREATE TABLE: Example
CREATE TABLE employees
( employee_id NUMBER(6)
CONSTRAINT emp_employee_id PRIMARY KEY
, first_name VARCHAR2(20)
, last_name VARCHAR2(25)
CONSTRAINT emp_last_name_nn NOT NULL
, email VARCHAR2(25)
CONSTRAINT emp_email_nn NOT NULL
CONSTRAINT emp_email_uk UNIQUE
, phone_number VARCHAR2(20)
, hire_date DATE
CONSTRAINT emp_hire_date_nn NOT NULL
, job_id VARCHAR2(10)
CONSTRAINT emp_job_nn NOT NULL
, salary NUMBER(8,2)
CONSTRAINT emp_salary_ck CHECK (salary>0)
, commission_pct NUMBER(2,2)
, manager_id NUMBER(6)
, department_id NUMBER(4)
CONSTRAINT emp_dept_fk REFERENCES
departments (department_id));


Violating Constraints

UPDATE employees
SET department_id = 55

UPDATE employees
*
ERROR at line 1:
ORA-02291: integrity constraint (HR.EMP_DEPT_FK)
violated - parent key not found

Department 55 does not exist.


Violating Constraints

You cannot delete a row that contains a primary key
that is used as a foreign key in another table.


*
ERROR at line 1:
ORA-02292: integrity constraint (HR.EMP_DEPT_FK)
violated - child record found


Creating a Table
by Using a Subquery

• Create a table and insert rows by combining the
CREATE TABLE statement and the AS subquery
option.
CREATE TABLE table
[(column, column...)]
AS subquery;

• Match the number of specified columns to the
number of subquery columns.
• Define columns with column names and
default values.


Creating a Table
by Using a Subquery

CREATE TABLE dept80
AS
SELECT employee_id, last_name,
salary*12 ANNSAL,
hire_date
FROM employees
Table created.

DESCRIBE dept80


ALTER TABLE Statement

Use the ALTER TABLE statement to:
• Add a new column
• Modify an existing column
• Define a default value for the new column
• Drop a column


Dropping a Table

• All data and structure in the table are deleted.
• Any pending transactions are committed.
• All indexes are dropped.
• All constraints are dropped.
• You cannot roll back the DROP TABLE statement.
DROP TABLE dept80;
Table dropped.


Summary

In this lesson, you should have learned how to use the
CREATE TABLE statement to create a table and include
constraints.
• Categorize the main database objects
• Review the table structure
• List the data types that are available for columns
• Create a simple table
• Understand how constraints are created at the
time of table creation
• Describe how schema objects work



• Creating new tables
• Creating a new table by using the CREATE TABLE
AS syntax
• Verifying that tables exist
• Dropping tables


Creating Other Schema Objects


Objectives

the following:
• Create simple and complex views
• Retrieve data from views
• Create, maintain, and use sequences
• Create and maintain indexes
• Create private and public synonyms


Database Objects

Object Description

one or more tables
queries


What Is a View?

EMPLOYEES table


Advantages of Views

To restrict To make complex
data access queries easy

To provide To present
data different views of
independence the same data


Simple Views and Complex Views

Feature Simple Views Complex Views
Number of tables One One or more
Contain functions No Yes
Contain groups of data No Yes
DML operations Yes Not always
through a view


Creating a View

• You embed a subquery in the CREATE VIEW
statement:
CREATE [OR REPLACE] [FORCE|NOFORCE] VIEW view
[(alias[, alias]...)]
AS subquery
[WITH CHECK OPTION [CONSTRAINT constraint]]
[WITH READ ONLY [CONSTRAINT constraint]];

• The subquery can contain complex SELECT
syntax.


Creating a View

• Create the EMPVU80 view, which contains details
of employees in department 80:
CREATE VIEW empvu80
AS SELECT employee_id, last_name, salary
FROM employees
View created.
• Describe the structure of the view by using the
iSQL*Plus DESCRIBE command:

DESCRIBE empvu80


Creating a View

• Create a view by using column aliases in the
subquery:
CREATE VIEW salvu50
AS SELECT employee_id ID_NUMBER, last_name NAME,
salary*12 ANN_SALARY
FROM employees
View created.

• Select the columns from this view by the given
alias names:


Retrieving Data from a View

SELECT *
FROM salvu50;


Modifying a View

• Modify the EMPVU80 view by using a CREATE OR
REPLACE VIEW clause. Add an alias for each
column name:
CREATE OR REPLACE VIEW empvu80
(id_number, name, sal, department_id)
AS SELECT employee_id, first_name || ' '
|| last_name, salary, department_id
FROM employees
View created.
• Column aliases in the CREATE OR REPLACE VIEW
clause are listed in the same order as the columns
in the subquery.


Creating a Complex View

Create a complex view that contains group functions
to display values from two tables:
CREATE OR REPLACE VIEW dept_sum_vu
(name, minsal, maxsal, avgsal)
AS SELECT d.department_name, MIN(e.salary),
MAX(e.salary),AVG(e.salary)
ON (e.department_id = d.department_id)
GROUP BY d.department_name;
View created.


Rules for Performing
DML Operations on a View

• You can usually perform DML operations
on simple views.
• You cannot remove a row if the view contains the
following:
– Group functions
– A GROUP BY clause
– The DISTINCT keyword
– The pseudocolumn ROWNUM keyword



You cannot modify data in a view if it contains:
• Group functions
• A GROUP BY clause
• The DISTINCT keyword
• The pseudocolumn ROWNUM keyword
• Columns defined by expressions



You cannot add data through a view if the view
includes:
• Group functions
• A GROUP BY clause
• The DISTINCT keyword
• The pseudocolumn ROWNUM keyword
• Columns defined by expressions
• NOT NULL columns in the base tables that are not
selected by the view


Using the WITH CHECK OPTION Clause

• You can ensure that DML operations performed on
the view stay in the domain of the view by using
the WITH CHECK OPTION clause:
AS SELECT *
FROM employees
WHERE department_id = 20
WITH CHECK OPTION CONSTRAINT empvu20_ck ;
View created.

• Any attempt to change the department number for
any row in the view fails because it violates the
WITH CHECK OPTION constraint.


Denying DML Operations

• You can ensure that no DML operations occur by
adding the WITH READ ONLY option to your view
definition.
• Any attempt to perform a DML operation on any
row in the view results in an Oracle server error.


Denying DML Operations

(employee_number, employee_name, job_title)
AS SELECT employee_id, last_name, job_id
FROM employees
WHERE department_id = 10
WITH READ ONLY ;
View created.


Removing a View

You can remove a view without losing data because a
view is based on underlying tables in the database.
DROP VIEW view;

DROP VIEW empvu80;
View dropped.



• Creating a simple view
• Creating a complex view
• Creating a view with a check constraint
• Attempting to modify data in the view
• Removing views


Sequences

Object Description

one or more tables
queries


Sequences

A sequence:
• Can automatically generate unique numbers
• Is a sharable object
• Can be used to create a primary key value
• Replaces application code
• Speeds up the efficiency of accessing sequence
values when cached in memory

2 4 6 8 10
1 3 5 7 9


CREATE SEQUENCE Statement:
Syntax

Define a sequence to generate sequential numbers
automatically:
CREATE SEQUENCE sequence
[INCREMENT BY n]
[START WITH n]
[{MAXVALUE n | NOMAXVALUE}]
[{MINVALUE n | NOMINVALUE}]
[{CYCLE | NOCYCLE}]
[{CACHE n | NOCACHE}];


Creating a Sequence

• Create a sequence named DEPT_DEPTID_SEQ to
be used for the primary key of the DEPARTMENTS
table.
• Do not use the CYCLE option.
CREATE SEQUENCE dept_deptid_seq
INCREMENT BY 10
START WITH 120
MAXVALUE 9999
NOCACHE
NOCYCLE;
Sequence created.


NEXTVAL and CURRVAL Pseudocolumns

• NEXTVAL returns the next available sequence
value. It returns a unique value every time it is
referenced, even for different users.
• CURRVAL obtains the current sequence value.
• NEXTVAL must be issued for that sequence before
CURRVAL contains a value.


Using a Sequence

• Insert a new department named “Support” in
location ID 2500:
INSERT INTO departments(department_id,
department_name, location_id)
VALUES (dept_deptid_seq.NEXTVAL,
'Support', 2500);
1 row created.

• View the current value for the DEPT_DEPTID_SEQ
sequence:
SELECT dept_deptid_seq.CURRVAL
FROM dual;


Caching Sequence Values

• Caching sequence values in memory gives faster
access to those values.
• Gaps in sequence values can occur when:
– A rollback occurs
– The system crashes
– A sequence is used in another table


Modifying a Sequence

Change the increment value, maximum value,
minimum value, cycle option, or cache option:

ALTER SEQUENCE dept_deptid_seq
INCREMENT BY 20
MAXVALUE 999999
NOCACHE
NOCYCLE;
Sequence altered.


Guidelines for Modifying
a Sequence

• You must be the owner or have the ALTER
privilege for the sequence.
• Only future sequence numbers are affected.
• The sequence must be dropped and
re-created to restart the sequence at a different
number.
• Some validation is performed.
• To remove a sequence, use the DROP statement:

DROP SEQUENCE dept_deptid_seq;
Sequence dropped.


Indexes

Object Description

one or more tables
queries


Indexes

An index:
• Is a schema object
• Can be used by the Oracle server to speed up the
retrieval of rows by using a pointer
• Can reduce disk I/O by using a rapid path access
method to locate data quickly
• Is independent of the table that it indexes
• Is used and maintained automatically by the
Oracle server


How Are Indexes Created?

• Automatically: A unique index is created
automatically when you define a PRIMARY KEY or
UNIQUE constraint in a table definition.

• Manually: Users can create nonunique indexes on
columns to speed up access to the rows.


Creating an Index

• Create an index on one or more columns:

CREATE INDEX index
ON table (column[, column]...);

• Improve the speed of query access to the
LAST_NAME column in the EMPLOYEES table:

CREATE INDEX emp_last_name_idx
ON employees(last_name);
Index created.


Index Creation Guidelines

Create an index when:
A column contains a wide range of values
A column contains a large number of null values
One or more columns are frequently used together in a WHERE
clause or a join condition
The table is large and most queries are expected to retrieve less
than 2% to 4% of the rows in the table
Do not create an index when:
The columns are not often used as a condition in the query
The table is small or most queries are expected to retrieve more
than 2% to 4% of the rows in the table
The table is updated frequently
The indexed columns are referenced as part of an expression


Removing an Index

• Remove an index from the data dictionary by
using the DROP INDEX command:

DROP INDEX index;

• Remove the UPPER_LAST_NAME_IDX index from
the data dictionary:
DROP INDEX emp_last_name_idx;
Index dropped.
• To drop an index, you must be the owner of the
index or have the DROP ANY INDEX privilege.


Synonyms

Object Description

one or more tables
queries


Synonyms

Simplify access to objects by creating a synonym
(another name for an object). With synonyms, you can:
• Create an easier reference to a table that is owned
by another user
• Shorten lengthy object names
CREATE [PUBLIC] SYNONYM synonym
FOR object;


Creating and Removing Synonyms

• Create a shortened name for the DEPT_SUM_VU
view:
CREATE SYNONYM d_sum
FOR dept_sum_vu;
Synonym Created.

• Drop a synonym:
DROP SYNONYM d_sum;
Synonym dropped.


Summary

• Create, use, and remove views
• Automatically generate sequence numbers by
using a sequence generator
• Create indexes to improve query retrieval speed
• Use synonyms to provide alternative names for
objects



• Creating sequences
• Using sequences
• Creating nonunique indexes
• Creating synonyms


Managing Objects
with Data Dictionary Views


Objectives

the following:
• Use the data dictionary views to research data on
your objects
• Query various data dictionary views


The Data Dictionary

Oracle server

Tables containing Data dictionary
business data: views:
EMPLOYEES DICTIONARY
DEPARTMENTS USER_OBJECTS
LOCATIONS USER_TABLES
JOB_HISTORY USER_TAB_COLUMNS
... ...


Data Dictionary Structure

Oracle server

Consists of:
– Base tables
– User-accessible views


Data Dictionary Structure

View naming convention:

View Prefix Purpose
USER User’s view (what is in your schema;
what you own)
ALL Expanded user’s view (what you can
access)
DBA Database administrator’s view (what is in
everyone’s schemas)
V$ Performance-related data


How to Use the Dictionary Views

Start with DICTIONARY. It contains the names and
descriptions of the dictionary tables and views.
DESCRIBE DICTIONARY

SELECT *
FROM dictionary
WHERE table_name = 'USER_OBJECTS';


USER_OBJECTS and ALL_OBJECTS Views

USER_OBJECTS:
• Query USER_OBJECTS to see all of the objects that
are owned by you
• Is a useful way to obtain a listing of all object
names and types in your schema, plus the
following information:
– Date created
– Date of last modification
– Status (valid or invalid)
ALL_OBJECTS:
• Query ALL_OBJECTS to see all objects to which
you have access


USER_OBJECTS View

SELECT object_name, object_type, created, status
FROM user_objects
ORDER BY object_type;

…


Table Information

USER_TABLES:
DESCRIBE user_tables

SELECT table_name
FROM user_tables;

…

Column Information

USER_TAB_COLUMNS:
DESCRIBE user_tab_columns

…


Column Information

SELECT column_name, data_type, data_length,
data_precision, data_scale, nullable
FROM user_tab_columns
WHERE table_name = 'EMPLOYEES';


Constraint Information

• USER_CONSTRAINTS describes the constraint
definitions on your tables.
• USER_CONS_COLUMNS describes columns that are
owned by you and that are specified in
constraints.
DESCRIBE user_constraints

…


SELECT constraint_name, constraint_type,
search_condition, r_constraint_name,
delete_rule, status
FROM user_constraints



DESCRIBE user_cons_columns

SELECT constraint_name, column_name
FROM user_cons_columns

…

View Information

1 DESCRIBE user_views

2 SELECT DISTINCT view_name FROM user_views;

SELECT text FROM user_views
3 WHERE view_name = 'EMP_DETAILS_VIEW';


Sequence Information

DESCRIBE user_sequences


Sequence Information

• Verify your sequence values in the
USER_SEQUENCES data dictionary table.
SELECT sequence_name, min_value, max_value,
increment_by, last_number
FROM user_sequences;

• The LAST_NUMBER column displays the next
available sequence number if NOCACHE is
specified.


Synonym Information

DESCRIBE user_synonyms

SELECT *
FROM user_synonyms;


Adding Comments to a Table

• You can add comments to a table or column by
using the COMMENT statement:
COMMENT ON TABLE employees
IS 'Employee Information';
Comment created.

• Comments can be viewed through the data
dictionary views:
– ALL_COL_COMMENTS
– USER_COL_COMMENTS
– ALL_TAB_COMMENTS
– USER_TAB_COMMENTS


Summary

In this lesson, you should have learned how to find
information about your objects through the following
dictionary views:
• DICTIONARY
• USER_OBJECTS
• USER_TABLES
• USER_TAB_COLUMNS
• USER_CONSTRAINTS
• USER_CONS_COLUMNS
• USER_VIEWS
• USER_SEQUENCES
• USER_TAB_SYNONYMS



• Querying the dictionary views for table and
column information
• Querying the dictionary views for constraint
information
• Querying the dictionary views for view information
• Querying the dictionary views for sequence
information
• Querying the dictionary views for synonym
information
• Adding a comment to a table and querying the
dictionary views for comment information


Oracle Join Syntax


Objectives

the following:
• Write SELECT statements to access data from
more than one table using equijoins and non-
equijoins
• Use outer joins to view data that generally does
not meet a join condition
• Join a table to itself by using a self-join


Cartesian Products

• A Cartesian product is formed when:
– A join condition is omitted
– A join condition is invalid
– All rows in the first table are joined to all rows in the
second table
• To avoid a Cartesian product, always include a
valid join condition in a WHERE clause.


Types of Joins

Oracle-proprietary joins SQL:1999–compliant joins
(8i and earlier releases)

• Equijoin • Cross join
• Non-equijoin • Natural join
• Outer join • Using clause
• Self-join • Full (or two-sided)
outer join
• Arbitrary join
condition for outer
join


Joining Tables Using Oracle Syntax

Use a join to query data from more than one table:

FROM table1, table2
WHERE table1.column1 = table2.column2;

• Write the join condition in the WHERE clause.
• Prefix the column name with the table name when
the same column name appears in more than one
table.


Equijoins


… …
Foreign key Primary key


Retrieving Records
with Equijoins

SELECT employees.employee_id, employees.last_name,
employees.department_id, departments.department_id,
departments.location_id
FROM employees, departments
WHERE employees.department_id = departments.department_id;

…


Additional Search Conditions
Using the AND Operator


… …


Qualifying Ambiguous Column Names

• Use table prefixes to qualify column names that
are in multiple tables.
• Use column aliases to distinguish columns that
have identical names but reside in different tables.


Using Table Aliases

• Use table aliases to simplify queries.

FROM employees e , departments d
WHERE e.department_id = d.department_id;


Joining More Than Two Tables

EMPLOYEES DEPARTMENTS LOCATIONS

…
To join n tables together, you need a minimum of n–1
join conditions. For example, to join three tables, a
minimum of two joins is required.


Retrieving Records
with Non-Equijoins

SELECT e.last_name, e.salary, j.grade_level
FROM employees e, job_grades j
WHERE e.salary
BETWEEN j.lowest_sal AND j.highest_sal;

…


Outer Joins

DEPARTMENTS EMPLOYEES

…
There are no employees
in department 190.


Outer Joins Syntax

• You use an outer join to see rows that do not meet
the join condition.
• The outer join operator is the plus sign (+).

FROM table1, table2
WHERE table1.column(+) = table2.column;

FROM table1, table2
WHERE table1.column = table2.column(+);


Using Outer Joins

FROM employees e, departments d
WHERE e.department_id(+) = d.department_id ;

…


Self-Joins

EMPLOYEES (WORKER) EMPLOYEES (MANAGER)

… …

MANAGER_ID in the WORKER table is equal to
EMPLOYEE_ID in the MANAGER table.


Joining a Table to Itself

SELECT worker.last_name || ' works for '
|| manager.last_name
FROM employees worker, employees manager
WHERE worker.manager_id = manager.employee_id ;

…


Summary

In this appendix, you should have learned how to use
joins to display data from multiple tables by using
Oracle-proprietary syntax for versions 8i and earlier.


Practice C: Overview

This practice covers writing queries to join tables
using Oracle syntax.


Using SQL*Plus


Objectives

After completing this appendix, you should be able to
do the following:
• Log in to SQL*Plus
• Edit SQL commands
• Format output using SQL*Plus commands
• Interact with script files


SQL and SQL*Plus Interaction

SQL statements
Server
SQL*Plus

Query results

Buffer

SQL
scripts


SQL Statements Versus
SQL*Plus Commands

SQL SQL*Plus
• A language • An environment
• ANSI-standard • Oracle-proprietary
• Keywords cannot be • Keywords can be
abbreviated abbreviated
• Statements manipulate • Commands do not
data and table allow manipulation of
definitions in the values in the database
database

SQL SQL SQL*Plus SQL*Plus
statements buffer commands buffer


Overview of SQL*Plus

• Log in to SQL*Plus.
• Describe the table structure.
• Edit your SQL statement.
• Execute SQL from SQL*Plus.
• Save SQL statements to files and append SQL
statements to files.
• Execute saved files.
• Load commands from file to buffer to edit.


Logging In to SQL*Plus

• From a Windows environment:

• From a command line:
sqlplus [username[/password
[@database]]]



Use the SQL*Plus DESCRIBE command to display the
structure of a table:

DESC[RIBE] tablename



SQL> DESCRIBE departments

Name Null? Type
----------------------- -------- ------------
DEPARTMENT_ID NOT NULL NUMBER(4)
DEPARTMENT_NAME NOT NULL VARCHAR2(30)
MANAGER_ID NUMBER(6)
LOCATION_ID NUMBER(4)


SQL*Plus Editing Commands

• A[PPEND] text
• C[HANGE] / old / new
• C[HANGE] / text /
• CL[EAR] BUFF[ER]
• DEL
• DEL n
• DEL m n


SQL*Plus Editing Commands

• I[NPUT]
• I[NPUT] text
• L[IST]
• L[IST] n
• L[IST] m n
• R[UN]
• n
• n text
• 0 text


Using LIST, n, and APPEND

SQL> LIST

1 SELECT last_name
2* FROM employees

SQL> 1

1* SELECT last_name

SQL> A , job_id

1* SELECT last_name, job_id

SQL> L

1 SELECT last_name, job_id
2* FROM employees


Using the CHANGE Command

SQL> L

1* SELECT * from employees

SQL> c/employees/departments

1* SELECT * from departments

SQL> L

1* SELECT * from departments


SQL*Plus File Commands

• SAVE filename
• GET filename
• START filename
• @ filename
• EDIT filename
• SPOOL filename
• EXIT


Using the SAVE and START Commands

SQL> L
1 SELECT last_name, manager_id, department_id
2* FROM employees
SQL> SAVE my_query

Created file my_query

SQL> START my_query
LAST_NAME MANAGER_ID DEPARTMENT_ID
------------------------- ---------- -------------
King 90
Kochhar 100 90
...
20 rows selected.


Summary

In this appendix, you should have learned how to use
SQL*Plus as an environment to do the following:

• Execute SQL statements
• Edit SQL statements
• Format output
• Interact with script files


Oracle 10g sql fundamentals i

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