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1Copyright Oracle Corporation, 2001. All rights reserved.

Writing Basic

SQL SELECT Statements

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1-2 Copyright Oracle Corporation, 2001. All rights reserved.

Objectives

After completing this lesson, you should be able todo the following:

List the capabilities of SQL SELECT statements

Execute a basic SELECT statement Differentiate between SQL statements and

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

SELECT identifies whatcolumns

FROMidentifies which table

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SELECT *FROM departments;

Selecting All Columns

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Selecting Specific Columns

SELECT department_id, location_idFROM 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 split

across lines.

Clauses are usually placed on separate lines.

Indents are used to enhance readability.

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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

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Arithmetic Expressions

Create expressions with number and date data byusing arithmetic operators.

Operator

+

-

*

/

Description

Add

Subtract

Multiply

Divide

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Using Arithmetic Operators

SELECT last_name, salary, salary + 300FROM employees;

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Operator Precedence

Multiplication and division take priority overaddition and subtraction.

Operators of the same priority are evaluated fromleft to right.

Parentheses are used to force prioritizedevaluation and to clarify statements.

** // ++ __

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Operator Precedence

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

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Using Parentheses

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

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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 zero or a blank space.

ECT last_name, job_id, salary, commission_pctM employees;

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SELECT last_name, 12*salary*commission_pctFROM employees;

Null Values

in Arithmetic Expressions

Arithmetic expressions containing a null valueevaluate 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 thecolumn name and alias

Requires double quotation marks if it contains

spaces or special characters or is case sensitive

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Using Column Aliases

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

SELECT last_name AS name, commission_pct commFROM employees;

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Concatenation Operator

A concatenation operator:

Concatenates columns or character strings toother columns

Is represented by two vertical bars (||) Creates a resultant column that is a character

expression

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Using the Concatenation Operator

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 dateincluded 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.

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Using Literal Character Strings

SELECT last_name ||' is a '||job_idAS "Employee Details"

FROM employees;

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Duplicate Rows

The default display of queries is all rows, including

duplicate rows.

SELECT department_idFROM employees;

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Eliminating Duplicate Rows

Eliminate duplicate rows by using the DISTINCTkeyword in the SELECT clause.

SELECT DISTINCT department_idFROM employees;

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SQL and iSQL*Plus Interaction

SQL statements

Oracleserver

Query resultsQuery resultsiSQL*Plus

commands

Client

Formatted report

InternetInternet

BrowserBrowser

iiSQL*PlusSQL*Plus

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SQL Statements Versus

iSQL*Plus Commands

SQLSQL

statementsstatements

SQL A language

ANSI standard

Keyword cannot beabbreviated

Statements manipulatedata and table definitionsin the database

iiSQL*PlusSQL*Plus An environment

Oracle proprietary

Keywords can beabbreviated

Commands do not allowmanipulation of values inthe database

Runs on a browser

Centrally loaded, does not

have to be implementedon each machine

iiSQL*PlusSQL*Plus

commandscommands

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Overview ofiSQL*Plus

After you log into iSQL*Plus, you can:

Describe the table structure

Edit your SQL statement

Execute SQL from iSQL*Plus

Save SQL statements to files and append SQLstatements to files

Execute statements stored in saved files

Load commands from a text file into the iSQL*PlusEdit window

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Logging In to iSQL*Plus

From your Windows browser environment:

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The iSQL*Plus Environment

3 4 5

6

71

2

8 910

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Displaying Table Structure

Use the iSQL*Plus DESCRIBE command to displaythe 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, salaryFROM employees; 1

2

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1

D:\temp\emp_sql.htm

2SELECT last_name, hire_date, salaryFROM employees;

3

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DESCRIBE employeesSELECT first_name, last_name, job_idFROM employees;

1

23

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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 columnheadings

Use the iSQL*Plus environment to write, save, andexecute SQL statements and iSQL*Plus commands.

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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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