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Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć240 minutes Lecture 25 minutes Practice 65 minutes Total Class Management Note: Files required for lesson are: Demonstrat

Selecting Rows

1

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć2

40 minutes Lecture

25 minutes Practice

65 minutes Total

Class Management Note:

Files required for lesson are:

Demonstration: l1prec1.sql, l1prec2.sql, l1alias.sql, l1null1.sql

Practice: None

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In order to extract data from the database you need to use the Structured Query Language (SQL) SELECT command You may need to restrict the columns that are displayed This lesson explains all of the commands you will use to perform these actions.

You will want to create SELECT statements that can be used time and time again In this lesson you will also see how to save your statements for later use.

At the end of this lesson, you should be able to

D Write a SELECT statement to query the database

D Perform arithmetic calculations using SQL arithmetic operators

D Handle null values

D Specify alternative column headings using aliases

D Concatenate columns

D Edit SQL statements in the SQL*Plus buffer and create command files

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć4

where: SELECT is a list of at least one column.

DISTINCT suppresses duplicates

* selects all columns

column selects the named column

alias gives selected columns a different heading

FROM table specifies the table containing the columns

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Writing SQL Commands

By following these simple rules and guidelines, you will be able to construct validstatements that are easy both to read and to edit

D SQL commands may be entered on one or many lines

D Clauses are usually placed on separate lines for readability and ease of editing

D Tabs and indents can be used to make code more readable

D Command words cannot be split across lines or abbreviated

D Keywords and commands typically are entered in uppercase; all other words,such as table names and columns, are entered in lowercase

D SQL commands are not case sensitive, unless indicated

D An SQL command is entered at the SQL prompt, and subsequent lines are

numbered This is called the SQL buffer.

D Only one statement can be current at any time within the buffer, and the

statement can be executed in a number of ways:

D Place a semicolon (;) at the end of last clause

D Place a semicolon or slash on the last line in the buffer

D Place a slash at the SQL prompt

D Issue a SQL*Plus RUN command at the SQL prompt

For more information, see

Oracle Applications: Coding Standards, Release 10G.

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Simplest SELECT statement contains the following two clauses:

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In its simplest form, a SELECT statement must include the following:

D A SELECT clause, which specifies the columns to be displayed

D A FROM clause, which specifies the table containing the columns listed in the SELECT clause

Selecting All Columns and Rows

The asterisk (*) selects all columns from the table

Example

List all columns and all rows from the S_DEPT table

SQL> SELECT *

2 FROM s_dept;

ID NAME REGION_ID

- -

10 Finance 1

31 Sales 1

32 Sales 2

33 Sales 3

34 Sales 4

35 Sales 5

41 Operations 1

42 Operations 2

43 Operations 3

44 Operations 4

45 Operations 5

50 Administration 1

12 rows selected

Class Management Note:

Let the students know that the details of all the tables are given in Appendix B

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Selecting Specific Columns

You restrict the query to display only certain columns by specifying the column names, separated by commas, in the SELECT clause

Example

Display all department numbers, employee last names, and manager numbers in the S_EMP table

SQL> SELECT dept_id, last_name, manager_id

2 FROM s_emp;

DEPT_ID LAST_NAME MANAGER_ID

-

50 Velasquez 41 Ngao 1

31 Nagayama 1

10 Quick-To-See 1

50 Ropeburn 1

41 Urguhart 2

42 Menchu 2

43 Biri 2

44 Catchpole 2

25 rows selected

Specify the columns you want to see, in the order in which you want to see them, in the SELECT clause Do not forget to use the comma as a column name separator

Column Heading Defaults

Character and date column headings and data are left-justified within a column and numbers are right-justified Character and date column headings may be truncated, but number headings may not be truncated The column labels appear in uppercase by default You can override the column label display with an alias

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You may need to modify the way data is displayed, perform calculations, or look atwhat-if scenarios This is possible using arithmetic expressions

An arithmetic expression may contain column names, constant numeric values, and

the arithmetic operators

Arithmetic Operators

These are the arithmetic operators available in SQL You may use arithmetic

operators in any clause of a SQL statement except the FROM clause

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć14

Class Management Note:

Let the students know that SQL*Plus ignores blank spaces before and afterthe arithmetic operator Formatting column values will be covered in laterlessons

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Operator Precedence

If an arithmetic expression contains more than one operator, multiplication and

division are evaluated first If operators within an expression are of the same priority,then evaluation is from left to right

Note: Use parentheses to reinforce the standard order of precedence and to improve

clarity For example, the expression above can be written as (12 * salary) +

100 with no change in the result

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć18

Class Management Note:

DEMO: l1prec1.sql, l1prec2.sql

PURPOSE: l1prec1.sql demonstrates the previous page’s example with no

parentheses Note the first couple rows of totals

Then, execute demo file l1prec2.sql, which demonstrates using the

parentheses to override the rules of precedence Note that the totals arelarger

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Override the rules of precedence with parentheses to specify the order in which

operators are executed

Example

Display the last name, salary, and annual compensation of employees Calculate the annual compensation as monthly salary plus a monthly bonus of $100, multiplied by 12

SQL> SELECT last_name, salary, 12 * (salary + 100)

2 FROM s_emp;

LAST_NAME SALARY 12*(SALARY+100)

- -

-Velasquez 2500 31200

Ngao 1450 18600

Nagayama 1400 18000

Quick-To-See 1450 18600

Ropeburn 1550 19800

Urguhart 1200 15600

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć20

Class Management Note:

DEMO: l1alias.sql.

PURPOSE: The column headings for each of the examples on the nextpage Demonstrate how to modify the file to demonstrate the other example

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When displaying the result of a query, SQL*Plus normally uses the selected column’sname as the heading In many cases, that heading may be difficult to understand oreven meaningless You can change a column’s heading by using a column alias.Specify the alias after the column in the SELECT list using a space as a separator Bydefault, alias headings will be forced to uppercase and cannot contain blank spaces,unless the alias is enclosed in double quotation marks (“ ”)

Example

Display the last name, salary, and annual compensation of employees Calculate theannual compensation as monthly salary plus a monthly bonus of $100, multiplied by

12 Name the column ANNUAL_SALARY

SQL> SELECT last_name, salary,

2 12 * (salary + 100) AS ANNUAL_SALARY

3 FROM s_emp;

Note: You can include the AS keyword before the alias name to comply with ANSI

SQL 92 standards

Column Aliases with Double Quotation Marks

If the alias contains spaces, special characters (such as # or $), or is case-sensitive,enclose the alias in double quotation marks (“ ”)

SQL> SELECT last_name, salary,

2 12 * (salary + 100) ”Annual Salary”

3 FROM s_emp;

Class Management Note:

Within a SQL statement, a column alias can be used in both the SELECTand the ORDER BY clauses You cannot use column aliases in the WHEREclause Both alias features comply with the ANSI SQL 92 standard Youcan use this method of achieving mixed case column headings for now In alater section, you can format headings using the SQL*Plus COLUMNcommand section

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You can link columns to other columns, arithmetic expressions, or constant values tocreate a character expression by using the concatenation operator (||) Columns oneither side of the operator are combined to make one single output column

Example

Display the full names of the employees with the heading Employees

SQL> SELECT first_name||last_name AS ”Employees”

The AS keyword before the alias name makes the SELECT clause easier to read

Class Management Note:

The resulting column is VARCHAR2 datatype

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A literal is any character, expression, or number included in the SELECT list that isnot a column name or a column alias It is printed for each row returned Literalstrings of free-format text can be included in the query result and are treated like acolumn in the SELECT list

Date and character literals must be enclosed within single quotation marks (‘ ’);

number literals must not

Example

Display the full names of the employees and their titles with the heading Employees

Be sure to add punctuation

SQL> SELECT first_name || ’ ’ || last_name

2 || ’, ’|| title ”Employees”

3 FROM s_emp;

Employees

-Carmen Velasquez, President

LaDoris Ngao, VP, Operations

Midori Nagayama, VP, Sales

Mark Quick-To-See, VP, Finance

Audry Ropeburn, VP, Administration

Molly Urguhart, Warehouse Manager

Class Management Note:

Point out to students that there is a blank space between single quotes in themiddle of first_name and last_name, in the select statement

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć26

Class Management Note:

Make sure everyone is aware of exactly what a null is

DEMO: l1null1.sql

PURPOSE: Demonstrates why sales representatives have values andeveryone else has a null No commission values exist for non-sales

representatives, therefore the calculation with null results in null

Currently, Oracle treats a character value with length of zero as null

However, this may not continue to be true in future versions of Oracle

A null value is not the same as zero or a space Zero is a number, and a space is acharacter.

Columns of any datatype can contain null values, unless the column was defined asNOT NULL or as PRIMARY KEY when the table was created

Null Values in Arithmetic Expressions

If any column value in an expression is null, the result is null For example, if youattempt to perform division with zero, you will get an error However, if you divide

by null, the result is null

Example

Display the last name, salary, title, and calculated commission

SQL> SELECT last_name, title,

Havel Warehouse Manager

Magee Sales Representative 140

Giljum Sales Representative 186.25

Sedeghi Sales Representative 151.5

Nguyen Sales Representative 228.75

Dumas Sales Representative 253.75

Maduro Stock Clerk

For more information, see

Oracle7 Server SQL Reference, Release 7.3, “Elements of SQL.”

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć28

expr2 is the target value for converting null.

Note: You can use the NVL function to convert any datatype, but the return value is

always the same as the datatype of expr1.

Example

To calculate values for all employees from the previous example, use the NVL

function to convert null values to zero

SQL> SELECT last_name, title,

2 salary * NVL(commission_pct,0)/100 COMM

3 FROM s_emp;

LAST_NAME TITLE COMM

-

-

Havel Warehouse Manager 0

Magee Sales Representative 186.25

Giljum Sales Representative 186.25

NVL Conversions for Various Datatypes

Datatype Conversion Example

NUMBER NVL(number_column,9)

DATE NVL(date_column,‘01-JAN-95’)

CHAR or VARCHAR2 NVL(character_column,‘Unavailable’)

Introduction to Oracle: SQL and PL/SQL Using Procedure Builder 1Ć30

1 At the prompt, enter: SELECT name FROM s_dept;

2 Show the students the duplicate rows in the output

3 At the prompt, enter: SELECT DISTINCT name FROM s_dept;

4 Now display the unique department names

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Unless you indicate otherwise, SQL*Plus displays the results of a query withouteliminating duplicate rows

Example Displaying All Rows

Display all department names in the S_DEPT table

The DISTINCT Keyword

To eliminate duplicate rows in the result, include the DISTINCT keyword in theSELECT clause immediately after the SELECT command word

Example Displaying Unique Rows

Display all unique department names in the S_DEPT table.

SQL> SELECT DISTINCT name

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DISTINCT with Multiple Columns

You can specify multiple columns after the DISTINCT qualifier The DISTINCTqualifier affects all selected columns

Example

Display all the different combinations of job titles and department numbers

SQL> SELECT DISTINCT dept_id, title

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In this lesson, you saw how SQL commands are executed within a product calledSQL*Plus SQL*Plus is a SQL and PL/SQL command execution environment withadditional features

You can use a number of SQL*Plus commands when writing even the most basic ofSQL statements This section covers some basic SQL*Plus commands to help you to

D Describe the table structure

D Edit SQL in the buffer

D Save files containing SQL for editing purposes

D Execute saved files

D Load SQL commands from a file into the SQL buffer

D Obtain online help

For more information, see

SQL*Plus User’s Guide and Reference, Release 3.3.

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How you invoke SQL*Plus depends upon which type of operating system or

windows environment you are running

Log In Through a Windows Environment

You double-click the SQL*Plus icon in the window manager, then enter the

username, password, and database, if required

Log In Through a Command Line Environment

Once you log on to your machine, at the operating system prompt enter the SQL*Pluscommand

sqlplus [username [/password [@database]]]

where: username is your database username

password is your database password If you enter your

password here, it is visible

@database is the database connect string

Note: To ensure the integrity of your password, do not enter it at the operating

system prompt Instead, only enter your username Enter your password at thePassword prompt

Once you are successfully logged in SQL*Plus, you see the following message:

SQL*Plus: Version 3.1.2 Production on Fri May 12th 15:31:32 1995 Copyright (c) Oracle Corporation 1979, 1992, All rights reserved SQL>