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Copyright 2006, Oracle. All rights reserved.
Retrieving Data Using
the SQL SELECT Statement
Copyright 2006, Oracle. All rights reserved.1 - 2
Objectives
After completing this lesson, you should be able to dothe following:
List the capabilities of SQL SELECT statements
Execute a basic SELECT statement
Differentiate between SQL statements andiSQL*Plus commands
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Capabilities of SQL SELECT Statements
SelectionProjection
Table 1 Table 2
Table 1Table 1
Join
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Basic SELECT Statement
SELECT identifies the columns to be displayed.
FROMidentifies the table containing those columns.
SELECT *|{[DISTINCT] column|expression [alias],...}
FROM table;
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Copyright 2006, Oracle. All rights reserved.1 - 5
Selecting All Columns
SELECT *
FROM departments;
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Selecting Specific Columns
SELECT department_id, location_id
FROM departments;
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Writing SQL Statements
SQL statements are not case sensitive.
SQL statements can be on one or more lines.
Keywords cannot be abbreviated or splitacross lines.
Clauses are usually placed on separate lines.
Indents are used to enhance readability.
In iSQL*Plus, SQL statements can optionally beterminated by a semicolon (;). Semicolons arerequired if you execute multiple SQL statements.
In SQL*Plus, you are required to end each SQLstatement with a semicolon (;).
Copyright 2006, Oracle. All rights reserved.1 - 8
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
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Copyright 2006, Oracle. All rights reserved.1 - 9
Arithmetic Expressions
Create expressions with number and date data by using
arithmetic operators.
Multiply*
Divide/
Subtract-
Add+
DescriptionOperator
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SELECT last_name, salary, salary + 300
FROM employees;
Using Arithmetic Operators
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SELECT last_name, salary, 12*salary+100
FROM employees;
Operator Precedence
SELECT last_name, salary, 12*(salary+100)
FROM employees;
1
2
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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;
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Copyright 2006, Oracle. All rights reserved.1 -13
SELECT last_name, 12*salary*commission_pct
FROM employees;
Null Valuesin Arithmetic Expressions
Arithmetic expressions containing a null value evaluate to
null.
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Defining a Column Alias
A column alias:
Renames a column heading
Is useful with calculations
Immediately follows the column name (There canalso be the optionalAS keyword between the
column name and alias.)
Requires double quotation marks if it containsspaces or special characters or if it is case
sensitive
Copyright 2006, Oracle. All rights reserved.1 -15
Using Column Aliases
SELECT last_name "Name" , salary*12 "Annual Salary"
FROM employees;
SELECT last_name AS name, commission_pct comm
FROM employees;
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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 characterexpression
SELECT last_name||job_id AS "Employees"
FROM employees;
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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 enclosedby single quotation marks.
Each character string is output once for eachrow returned.
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Using Literal Character Strings
SELECT last_name ||' is a '||job_idAS "Employee Details"
FROM employees;
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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;
Copyright 2006, Oracle. All rights reserved.1 -20
Duplicate Rows
The default display of queries is all rows, includingduplicate rows.
SELECT department_id
FROM employees;
SELECT DISTINCT department_id
FROM employees;
1
2
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Copyright 2006, Oracle. All rights reserved.1 -21
SQL and iSQL*Plus Interaction
SQL statements
Query resultsiSQL*Pluscommands
Client
Formatted report
Internetbrowser
Oracleserver
Copyright 2006, Oracle. All rights reserved.1 -22
SQL Statements VersusiSQL*Plus Commands
SQLstatements
SQL
A language
ANSI standard
Keyword cannot beabbreviated
Statements manipulatedata and table definitionsin the database
iSQL*Plus
An environment
Oracle-proprietary
Keywords can beabbreviated
Commands do not allowmanipulation of values inthe database
Runs on a browser
Centrally loaded; does nothave to be implemented
on each machine
iSQL*Pluscommands
Copyright 2006, Oracle. All rights reserved.1 -23
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 savedscript files
Copyright 2006, Oracle. All rights reserved.1 -24
Logging In to iSQL*Plus
From your browser environment:
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iSQL*Plus Environment
6
3 4 5
1
2
8 9
7
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Displaying Table Structure
Use the iSQL*Plus DESCRIBE command to display the
structure of a table:
DESC[RIBE] tablename
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Displaying Table Structure
DESCRIBE employees
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Interacting with Script Files
SELECT last_name, hire_date, salary
FROM employees; 1
2
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Interacting with Script Files
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Interacting with Script Files
1
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Interacting with Script Files
2
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D:\TEMP\emp_data.sql
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iSQL*Plus History Page
1
2
3
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iSQL*Plus History Page
3
4
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Setting iSQL*Plus Preferences
2
3
1
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Setting the Output Location Preference
1
2
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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 descriptivecolumn headings
Use the iSQL*Plus environment to write, save, andexecute SQL statements and iSQL*Plus commands
SELECT *|{[DISTINCT] column|expression [alias],...}
FROMtable;
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Copyright 2006, Oracle. All rights reserved.1 -37
Practice 1: Overview
This practice covers the following topics:
Selecting all data from different tables
Describing the structure of tables
Performing arithmetic calculations and specifyingcolumn names
Using iSQL*Plus
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