Unit-3-SQL-part1.ppt

Authors: Elmasri and Navathe
Fundamentals of Database Systems , 7e
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CHAPTER 6
Basic SQL

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Chapter 6 Outline
 SQL Data Definition and Data Types
 Specifying Constraints in SQL
 Basic Retrieval Queries in SQL
 INSERT, DELETE, and UPDATE Statements in
SQL
 Additional Features of SQL

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Basic SQL
 SQL language
 Considered one of the major reasons for the
commercial success of relational databases
 SQL
 The origin of SQL is relational predicate calculus called
tuple calculus (see Ch.8) which was proposed initially
as the language SQUARE.
 SQL Actually comes from the word “SEQUEL” which was the
original term used in the paper: “SEQUEL TO SQUARE” by
Chamberlin and Boyce. IBM could not copyright that term, so they
abbreviated to SQL and copyrighted the term SQL.
 Now popularly known as “Structured Query language”.
 SQL is an informal or practical rendering of the
relational data model with syntax

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SQL Data Definition, Data Types,
Standards
 Terminology:
 Table, row, and column used for relational model
terms relation, tuple, and attribute
 CREATE statement
 Main SQL command for data definition
 Base tables (base relations)
 Relation and its tuples are actually created and
stored as a file by the DBMS

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The CREATE TABLE Command in
SQL
 Specifying a new relation
 Provide name of table
 Specify attributes, their types and initial
constraints
 General Format
 CREATE TABLE <Table Name> (Attribute1 type
constraint, Attribute2 type constraint, ……….);
 Eg:
 CREATE TABLE EMPLOYEE (EmpNo Char(4)
NOT NULL, Ename Varchar2(20),Bpay
number(8,2));

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Attribute Data Types in SQL
 Basic data types
 Numeric data types
 Integer numbers: INTEGER, INT, and SMALLINT
 Floating-point (real) numbers: FLOAT or REAL, and
DOUBLE PRECISION
 Character-string data types
 Fixed length: CHAR(n), CHARACTER(n)
 Varying length: VARCHAR(n), CHAR
VARYING(n), CHARACTER VARYING(n)

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Attribute Data Types and Domains in
SQL (cont’d.)
 Bit-string data types
 Fixed length: BIT(n)
 Varying length: BIT VARYING(n)
 Boolean data type
 Values of TRUE or FALSE or NULL
 DATE data type
 Ten positions
 Components are YEAR, MONTH, and DAY in the
form YYYY-MM-DD
 Multiple mapping functions available in RDBMSs to
change date formats

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Attribute Data Types and Domains in
SQL (cont’d.)
 Additional data types
 Timestamp data type
Includes the DATE and TIME fields
 Plus a minimum of six positions for decimal
fractions of seconds
 Optional WITH TIME ZONE qualifier
 INTERVAL data type
 Specifies a relative value that can be used to
increment or decrement an absolute value of a date,
time, or timestamp
 DATE, TIME, Timestamp, INTERVAL data types can
be cast or converted to string formats for comparison.

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INSERT
 In its simplest form, it is used to add one or more
tuples to a relation
 Attribute values should be listed in the same
order as the attributes were specified in the
CREATE TABLE command
 Constraints on data types are observed
automatically
 Any integrity constraints as a part of the DDL
specification are enforced

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The INSERT Command
 Specify the relation name and a list of values for
the tuple. All values including nulls are supplied.
 The variation below inserts multiple tuples where a new table is
loaded values from the result of a query.

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INSERT – add or insert raw into a
table
General format of INSERT
INSERT INTO <table name> VALUES
(value1,value2,value3,………);
Numeric values – just enter the number eg 25
String data – value insider “ “ eg: “Saji”

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Eg; INSERT COMMAND
CREATE TABLE student (stno number(2), name
char(20), m1 number (4,2), m2 number (4,2), m3
number(4,2));
INSERT INTO student VALUES
(01,”Mahesh”,,35,40.75);

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SELECT Command -
 To Display the content of a table
Format of command
SELECT < */list of columns/formula> FROM <table
name>;
* - display all columns values
list of columns – displaying required columns values
only
Formula – the value of the formula will be displayed

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 Student - stno,name,m1,m2,m3
To display the whole table content
 SELECT * FROM student;
To display the content of stno and m2
SELECT stno,m2 FROM student;
To display the content name, total mark
SELECT name,m1+m2+m3 FROM student;

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The SELECT-FROM-WHERE
Structure of Basic SQL Queries
 Basic form of the SELECT statement:

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The SELECT-FROM-WHERE Structure
of Basic SQL Queries (cont’d.)
 Logical comparison operators
 =, <, <=, >, >=, and <>
Eg: Select * from student where
M1>20 AND M2>20;
 Two simple condition can be combined by
using AND and OR operator
 AND – combined condition true when both
conditions are true
 Eg: Select * from student where M1>=20
AND m2>=20;

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(2+4)*6

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AND , OR operator in SELECT
 OR – combined condition true when either of
the conditions are true
 Eg: Select * from student where M1>20
OR m2>20;
Changing Priority order by using bracket
AND operator will get higher priority than OR
To change the priority bracket can be used
Select * from Employee where dept = ‘Sales’ AND
desig =‘Manager’ OR bpay > 5000

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AND , OR operator in SELECT
To change the priority bracket can be used
Select * from Employee where dept = ‘Sales’ AND dept
=‘Purchase’ OR bpay > 5000
Select * from Employee where dept = ‘Sales’ AND (dept
=‘Purchase’ OR bpay > 5000)

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Avoiding Duplicates
 SELET DISTINCT dept from Employee;
- Display the different dept from Employee
Using IN and NOT IN operator
SELECT * FROM employee where dept IN
(‘Sales’,’Purchase’,’FINACE’)
SELECT * FROM employee where dept NOT IN
(‘Sales’,’Purchase’)

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Using BETWEEN operator
 Select * from Student where M1>20 and M1<40;

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Sorting Records in a table – ORDER BY
SELECT * FROM STUDENT ORDER BY M1;
- Sorting student records in ascending order of
M1
SELECT * FROM STUDENT ORDER BY NAME
DESC; - descending order of Name

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Sorting Records in a table – ORDER
BY
 SELECT * FROM STUDENT ORDER BY NAME
ASC, M1 DESC; - ASCENDIG ORDER OF NAME
AND WHEN NAME REPEATS IN DESCENDING
ORDER OF M1
 SELECT * FROM STUDENT WHERE M1>25
ORDER BY M1; - using where clause to selectively
choose records and then sorting

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UPDATE
UPDATE <Table Name> SET
<attribute>=‘value/Expression’ [WHERE clause];
 Used to modify attribute values of one or more
selected tuples
 A WHERE-clause selects the tuples to be
modified
 An additional SET-clause specifies the attributes
to be modified and their new values
 Each command modifies tuples in the same
relation

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UPDATE (contd.)
 Example: Give all employees with empno 10, to10% raise
in salary.
UPDATE EMPLOYEE
SET BPAY = BPAY *1.1
WHERE EMPNO = 10;
 In this request, the modified SALARY value depends on
the original SALARY value in each tuple

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UPDATE (contd.)
 Example: Change the location and controlling
department number of project number 10 to
'Bellaire' and 5, respectively
UPDATE PROJECT
SET PLOCATION = 'Bellaire',
DNUM = 5
WHERE PNUMBER=10

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DELETE
 Removes tuples from a relation
 DELETE <Table Name> [WHERE clause];
 Includes a WHERE-clause to select the tuples to be
deleted
 Tuples are deleted from only one table at a time
 A missing WHERE-clause specifies that all tuples in
the relation are to be deleted; the table then becomes
an empty table
 The number of tuples deleted depends on the number
of tuples in the relation that satisfy the WHERE-clause

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The DELETE Command
 Removes tuples from a relation
 Includes a WHERE clause to select the tuples to be
deleted. The number of tuples deleted will vary.

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Specifying Constraints in SQL
Basic constraints:
 Relational Model has 3 basic constraint types that
are supported in SQL:
 Key constraint: A primary key value cannot be
duplicated
 Entity Integrity Constraint: A primary key value
cannot be null
 Referential integrity constraints : The “foreign key
“ must have a value that is already present as a
primary key, or may be null.

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Specifying Attribute Constraints
Other Restrictions on attribute domains:
 Default value of an attribute
DEFAULT <value>
NULL is not permitted for a particular attribute
(NOT NULL)
 CHECK clause
Dnumber INT NOT NULL CHECK (Dnumber >
0 AND Dnumber < 21);

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Specifying Key and Referential
Integrity Constraints
 PRIMARY KEY clause
 Specifies one or more attributes that make up the
primary key of a relation
 Dnumber INT PRIMARY KEY;
 UNIQUE clause
 Specifies alternate (secondary) keys (called
CANDIDATE keys in the relational model).
 Dname VARCHAR(15) UNIQUE;

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Specifying Key and Referential
Integrity Constraints (cont’d.)
 FOREIGN KEY clause
 Default operation: reject update on violation
 Attach referential triggered action clause
 Options include SET NULL, CASCADE, and SET
DEFAULT
 Action taken by the DBMS for SET NULL or SET
DEFAULT is the same for both ON DELETE and ON
UPDATE
 CASCADE option suitable for “relationship” relations

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Giving Names to Constraints
 Using the Keyword CONSTRAINT
 Name a constraint
 Useful for later altering

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Default attribute values and referential
integrity triggered action specification (Fig.
6.2)

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Specifying Constraints on Tuples
Using CHECK
 Additional Constraints on individual tuples within a
relation are also possible using CHECK
 CHECK clauses at the end of a CREATE TABLE
statement
 Apply to each tuple individually
 CHECK (Dept_create_date <=
Mgr_start_date);

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Basic Retrieval Queries in SQL
 SELECT statement
 One basic statement for retrieving information from
a database
 SQL allows a table to have two or more tuples
that are identical in all their attribute values
 Unlike relational model (relational model is strictly
set-theory based)
 Multiset or bag behavior
 Tuple-id may be used as a key

Unit-3-SQL-part1.ppt

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