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1
Copyright © Oracle Corporation, 2001. All rights reserved.
Writing Basic
SQL SELECT Statements

1-2 Copyright © Oracle Corporation, 2001. All rights reserved.
Objectives
After completing this lesson, you should be able to
do 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
Selection
Projection
Table 1 Table 2
Table 1
Table 1
Join

Basic SELECT Statement
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
• SELECT identifies what columns
• FROM identifies which table

SELECT *
FROM departments;
Selecting All Columns

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.

Column Heading Defaults
• iSQL*Plus:
– Default heading justification: Center
– Default heading display: Uppercase
• SQL*Plus:
– Character and Date column headings are left-
justified
– Number column headings are right-justified
– 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
• Multiplication and division take priority over
addition and subtraction.
• Operators of the same priority are evaluated from
left to right.
• Parentheses are used to force prioritized
evaluation and to clarify statements.
* / + _

Operator Precedence
SELECT last_name, salary, 12*salary+100
FROM employees;
…

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

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

SELECT last_name, 12*salary*commission_pct
FROM employees;
Null Values
in Arithmetic Expressions
Arithmetic expressions containing a null value
evaluate to null.
…
…

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 is case sensitive

Using Column Aliases
SELECT last_name "Name", salary*12 "Annual
Salary"
FROM employees;
SELECT last_name AS name,
commission_pct comm
FROM employees;
…
…

Concatenation Operator
A concatenation operator:
• Concatenates columns or character strings to
other columns
• Is represented by two vertical bars (||)
• Creates a resultant column that is a character
expression

Using the Concatenation Operator
SELECT last_name||job_id AS "Employees"
FROM employees;
…

Literal Character Strings
• A literal is a character, a number, or a date
included in the SELECT list.
• Date and character literal values must be enclosed
within 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;
…

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

Eliminating Duplicate Rows
Eliminate duplicate rows by using the DISTINCT
keyword in the SELECT clause.
SELECT DISTINCT department_id
FROM employees;

Displaying Table Structure
Use the iSQL*Plus DESCRIBE command to display
the structure of a table.
DESC[RIBE] tablename

Displaying Table Structure
DESCRIBE employees

Summary
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
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 give descriptive column
headings
• Use the iSQL*Plus environment to write, save, and
execute SQL statements and iSQL*Plus commands.

Practice
• Refer to the Lab book for the Practice Exercises

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