Writing Basic Sql Select Statements: Reserved

1

Writing Basic SQL SELECT Statements

Copyright © Oracle Corporation, 2001. All rights

Objectives After completing this lesson, you should be able to do the following:

• • •

1-2

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

Copyright © Oracle Corporation, 2001. All rights

Capabilities of SQL SELECT Statements Projection

Selection

Table 1

Table 1 Join

Table 1 1-3

Table 2 Copyright © Oracle Corporation, 2001. All rights

Basic SELECT Statement

SELECT FROM

• •

1-4

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

SELECT identifies what columns FROM identifies which table

Copyright © Oracle Corporation, 2001. All rights

Selecting All Columns

SELECT * FROM departments;

1-5

Copyright © Oracle Corporation, 2001. All rights

Selecting Specific Columns

SELECT department_id, location_id FROM departments;

1-6

Copyright © Oracle Corporation, 2001. All rights

Writing SQL Statements

1-7

• • •

SQL statements are not case sensitive.

• •

Clauses are usually placed on separate lines.

SQL statements can be on one or more lines. Keywords cannot be abbreviated or split across lines. Indents are used to enhance readability.

Copyright © Oracle Corporation, 2001. All rights

Column Heading Defaults • •

1-8

iSQL*Plus: –

Default heading justification: Center

–

Default heading display: Uppercase

SQL*Plus: –

Character and Date column headings are leftjustified

–

Number column headings are right-justified

–

Default heading display: Uppercase

Copyright © Oracle Corporation, 2001. All rights

Arithmetic Expressions Create expressions with number and date data by using arithmetic operators. Operator

1-9

Description

+

Add

-

Subtract

*

Multiply

/

Divide

Copyright © Oracle Corporation, 2001. All rights

Using Arithmetic Operators SELECT last_name, salary, salary + 300 FROM employees;

…

1-10

Copyright © Oracle Corporation, 2001. All rights

Operator Precedence

* / +

1-11

_

•

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.

Copyright © Oracle Corporation, 2001. All rights

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

…

1-12

Copyright © Oracle Corporation, 2001. All rights

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

…

1-13

Copyright © Oracle Corporation, 2001. All rights

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.

LECT last_name, job_id, salary, commission_pct OM employees;

… …

1-14

Copyright © Oracle Corporation, 2001. All rights

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

… …

1-15

Copyright © Oracle Corporation, 2001. All rights

Defining a Column Alias A column alias:

1-16

• • •

Renames a column heading

•

Requires double quotation marks if it contains spaces or special characters or is case sensitive

Is useful with calculations Immediately follows the column name - there can also be the optional AS keyword between the column name and alias

Copyright © Oracle Corporation, 2001. All rights

Using Column Aliases SELECT last_name AS name, commission_pct comm FROM employees;

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

…

1-17

Copyright © Oracle Corporation, 2001. All rights

Concatenation Operator A concatenation operator:

1-18

•

Concatenates columns or character strings to other columns

• •

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

Copyright © Oracle Corporation, 2001. All rights

Using the Concatenation Operator

SELECT FROM

last_name||job_id AS "Employees" employees;

…

1-19

Copyright © Oracle Corporation, 2001. All rights

Literal Character Strings

1-20

•

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.

Copyright © Oracle Corporation, 2001. All rights

Using Literal Character Strings

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

…

1-21

Copyright © Oracle Corporation, 2001. All rights

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

…

1-22

Copyright © Oracle Corporation, 2001. All rights

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

1-23

Copyright © Oracle Corporation, 2001. All rights

SQL and iSQL*Plus Interaction SQL statements

iSQL*Plus

Oracle server

Internet Browser

Query results

iSQL*Plus commands Formatted report Client

1-24

Copyright © Oracle Corporation, 2001. All rights

SQL Statements Versus iSQL*Plus Commands SQL • A language • ANSI standard • Keyword cannot be abbreviated • Statements manipulate data and table definitions in the database

SQL statements 1-25

iSQL*Plus • An environment • Oracle proprietary • Keywords can be abbreviated • Commands do not allow manipulation of values in the database • Runs on a browser • Centrally loaded, does not have to be implemented on each machine iSQL*Plus commands

Copyright © Oracle Corporation, 2001. All rights

Overview of iSQL*Plus After you log into iSQL*Plus, you can:

1-26

• • • •

Describe the table structure

• •

Execute statements stored in saved files

Edit your SQL statement Execute SQL from iSQL*Plus Save SQL statements to files and append SQL statements to files Load commands from a text file into the iSQL*Plus Edit window

Copyright © Oracle Corporation, 2001. All rights

Logging In to iSQL*Plus From your Windows browser environment:

1-27

Copyright © Oracle Corporation, 2001. All rights

The iSQL*Plus Environment 10

9

8

6

7

1 2

1-28

3

Copyright © Oracle Corporation, 2001. All rights

4

5

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

1-29

Copyright © Oracle Corporation, 2001. All rights

Displaying Table Structure

DESCRIBE employees

1-30

Copyright © Oracle Corporation, 2001. All rights

Interacting with Script Files

SELECT last_name, hire_date, salary FROM employees;

1 2

1-31

Copyright © Oracle Corporation, 2001. All rights

Interacting with Script Files 1 D:\temp\emp_sql.htm

SELECT last_name, hire_date, salary FROM employees;

3

1-32

Copyright © Oracle Corporation, 2001. All rights

2

Interacting with Script Files

DESCRIBE employees SELECT first_name, last_name, job_id FROM employees;

3

1-33

2

Copyright © Oracle Corporation, 2001. All rights

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 give descriptive column headings

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

SELECT FROM

1-34

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

Copyright © Oracle Corporation, 2001. All rights

Practice 1 Overview This practice covers the following topics:

1-35

• • •

Selecting all data from different tables

•

Using iSQL*Plus

Describing the structure of tables Performing arithmetic calculations and specifying column names

Copyright © Oracle Corporation, 2001. All rights

1-36

Copyright © Oracle Corporation, 2001. All rights

1-37

Copyright © Oracle Corporation, 2001. All rights

1-38

Copyright © Oracle Corporation, 2001. All rights

1-39

Copyright © Oracle Corporation, 2001. All rights

1-40

Copyright © Oracle Corporation, 2001. All rights