Oracle SQL Plus The Definitive Guide- P6 pptx

Here is an example showing how the PASSWORD command is used: SQL> PASSWORD Changing password for JONATHAN Old password: ******* New password: ******* Retype new password: ****** Password

There are some optional arguments to the EXIT command, which may be used to return success or failure values to the

operating system These are useful when running scripts in batch mode, and are described fully in Chapter 7, Advanced

Scripting.

Password

The PASSWORD command allows you to change your database password

The PASSWORD command was introduced beginning with SQL*Plus version 8 In prior versions, you need to use the ALTER USER command to change a password To change other people's passwords, you need the ALTER USER system privilege

The syntax for the PASSWORD command is:

PASSWORD [username]

where:

PASSW[ORD]

May be abbreviated to PASSW

username

Is the user whose password you want to change Usually only database administrators (DBAs) can change passwords for other users You do not need to supply a username if you are changing your own password

Here is an example showing how the PASSWORD command is used:

SQL> PASSWORD

Changing password for JONATHAN

Old password: *******

New password: *******

Retype new password: ******

Password changed

If you are running a version of SQL*Plus prior to version 8, the PASSWORD command will not be available Instead, use the ALTER USER command to change your password Here's how:

SQL> ALTER USER jonathan IDENTIFIED BY wonker;

As you can see, the PASSWORD command has the advantage of not showing the new password on the screen

The HELP command is used to get help on SQL statements, SQL*Plus commands, and PL/SQL commands

SQL*Plus 8.1, released with Oracle8i, provides help only on SQL*Plus commands This is because there wasn't time for Oracle to update the help text to cover all the new functionality in SQL and PL/SQL in time for the 8i release Subsequent versions of SQL*Plus should reenable SQL and PL/SQL help

The syntax for HELP is:

HELP [topic]

where:

Help

May not be abbreviated

topic

Is the help topic you want to read about Most SQL commands, SQL*Plus commands and PL/SQL statements are valid help topics There are others as well Entering HELP MENU will get you a complete list of valid topics

Help is not available on all implementations The Windows versions of SQL*Plus simply don't implement the feature Under Unix, the HELP command will work only if your DBA has installed that feature in the database You will know SQL*Plus help has not been installed if you enter the HELP command and get the results shown in this example:

SQL> HELP

HELP not accessible

SQL*Plus reads help text from a database table named HELP, owned by the user SYSTEM You will get the HELP not accessible message if that table does not exist, or if SQL*Plus cannot select from it because of some other problem Assuming the help feature has been installed, you can get a list of the various help topics available by using the HELP MENU command

Beginning with version 8.1 of SQL*Plus, you need to use HELP INDEX instead of HELP MENU

Here's an example of how HELP MENU can be used to get a list of help topics:

SQL> HELP MENU

Menu

SQL TOPICS PL/SQL TOPICS FUNCTIONS SQL*PLUS TOPICS

- - - -

alias attributes 1 row number help

comments blocks 1 row char commands

conditions commands conversion old commands

data dictionary cursors data functions overview

The HELP command is not available from the Windows versions of SQL*Plus If you are running in a Windows 95 or NT environment, you will need

to refer to the appropriate Oracle manuals for information on SQL*Plus, SQL, and PL/SQL commands These manuals are available on the distribution CD-ROM, and, beginning with version 7.3.3, are in HTML format

After identifying a topic of interest, you can get further help by using that topic name as an argument to the HELP

command Here is the information HELP gives you about the DESCRIBE command:

SQL> HELP DESCRIBE

DESCRIBE

DESC[RIBE] { [USER.]table[@database_link_name] [column] ¦

[user.] object[.subobject]}

DESCRIBE lists the column definitions for a table, view, or synonym,

or the specifications for a function, procedure, package, or

package contents

Entering HELP without an argument will get you help on using HELP

If you are running under Windows NT or 95, Oracle prefers to point you to the manual set included on the distribution CD-ROM The HELP command itself will still work; however, you will get the dialog box shown in Figure 2-6, which points you to the documentation on the CD-ROM

On most Oracle distribution CD-ROMs, you can get to the HTML documentation by opening a file named INDEX.HTM

in the DOC directory.

Figure 2-6

The No Help dialog

Describe

The DESCRIBE command lists the column definitions for a database table It can also be used to view procedure,

function, package, and object definitions If you have created and loaded the sample tables described in Chapter 1,

Introduction to SQL*Plus, you can use the DESCRIBE command to view their column definitions The following

example shows how DESCRIBE is used to list the columns in the EMPLOYEE table:

SQL> DESCRIBE employee

Name Null? Type

- -

EMPLOYEE_ID NOT NULL NUMBER

EMPLOYEE_NAME VARCHAR2(40)

EMPLOYEE_HIRE_DATE DATE

EMPLOYEE_TERMINATION_DATE DATE

EMPLOYEE_BILLING_RATE NUMBER

As you can see, the command lists three things for each column in the table:

The column's name

The column's datatype, and length if applicable

Whether or not the column can be null

See Chapter 6, Exploring Your Database, for more information about DESCRIBE, including examples of its use against

procedures, functions, packages, synonyms, and object types

Connect

The CONNECT command lets you log into your database as a different user, or log into a completely different

database It's useful if you develop against, or manage, more than one database, because you can quickly switch

between them when you need to It's also quite common for a developer or DBA to have multiple usernames on one database, with each being used for a different purpose A DBA

might log in as SYSTEM in order to create users and manage tablespaces, but might choose to log in with a less

privileged username when running reports

The complete syntax for CONNECT is:

CONNECT [username[/password] [@connect] ¦/

¦] [AS {SYSCOPER¦SYSDBA}] ¦ [INTERNAL]

where:

CONN[ECT]

May be abbreviated CONN

username

Is your database username

password

Is your database password

connect

Is the connect string, or host string, telling SQL*Plus the database to which you want to connect

/ Use a forward slash instead of your username, password, and connect string when you want to connect to a local database using operating system authentication

AS Tells SQL*Plus that you are connecting in an administrative role.

SYSOPER

Tells SQL*Plus that you are connecting as an operator

SYSDBA

Tells SQL*Plus that you are connecting as a database administrator

INTERNAL

Tells SQL*Plus that you want to connect internally

Everything beginning with the keyword AS applies when you are using SQL*Plus for database administration tasks Chapter 10 is devoted to that subject, and explains the use of the SYSOPER, SYSDBA, and INTERNAL keywords The simplest way to use the CONNECT command is to use it by itself, with no arguments, as shown here:

SQL> CONNECT

Enter user-name: jonathan

Enter password: *******

Connected

In the case above, SQL*Plus prompted for both a username and a password Notice, too, that the password characters

were echoed back as asterisks This prevents anyone from looking over your shoulder as you type and stealing your

word SQL*Plus did not prompt for a connect string, and won't, either, so using the above method only allows you to connect to your default database

Another form of the CONNECT command allows you to specify the username, password, and connect string all on one line This is the version I use most frequently as I switch back and forth between databases that I manage For example:

SQL> CONNECT system/driveway@plum

Connected

If you are security conscious (you should be) and happen to have someone looking over your shoulder, you may omit the password and let SQL*Plus prompt you for it The advantage here is that the password characters will be echoed to the screen as asterisks For example:

SQL> CONNECT system@oak

Enter password:*******

Connected

In at least one version of SQL*Plus version 8.0.4, there is a bug that keeps this from working You can enter CONNECT with the username as an argument, then enter the password when prompted, but SQL*Plus won't pass the correct information to the database

Go ahead and try the CONNECT command a few times, trying the variations shown above If you only have one

username you can use, try reconnecting as yourself just to get the hang of it

Disconnect

The DISCONNECT command is one I rarely use It's the analog of the CONNECT command, and simply disconnects you from the Oracle database while leaving you in SQL*Plus The syntax is very simple, and looks like this:

DISCONNECT

where:

DISC[ONNECT]

May be abbreviated to DISC

Here is an example of the DISCONNECT command being used:

SQL> DISCONNECT

Disconnected from Personal Oracle8 Release 8.0.3.0.0 - Production

With the Partitioning option

PL/SQL Release 8.0.3.0.0 - Production

SQL>

Any pending transactions are committed before you are disconnected from Oracle At this point you have three choices:

1 Reconnect to Oracle using the CONNECT command

2 Exit SQL*Plus

3 Execute SQL*Plus commands that do not require a database connection The SET command, for example, does not require you to be connected

DISCONNECT is useful if you want to leave a SQL*Plus session open for a long period of time, but do not wish to tie

up a database connection

Running SQL Queries

Using SQL*Plus, you can execute any SQL query or command that you desire This includes data manipulation

commands such as INSERT, UPDATE, DELETE, and SELECT This also includes data definition commands such as CREATE TABLE, CREATE INDEX, CREATE USER, etc Essentially, you can execute any command listed in the Oracle SQL reference manual

Here is an example of a simple SELECT statement against the PROJECT table:

SQL> SELECT * /* All Columns */

2 FROM project;

PROJECT_ID PROJECT_NAME PROJECT_BUDGET

- - -

1001 Corporate Web Site 1912000

1002 Year 2000 Fixes 999998000

1003 Accounting System Implementation 897000

1004 Data Warehouse Maintenance 294000

1005 TCP/IP Implementation 415000

Look again at the SELECT query shown above Notice that the statement spans more than one line Notice that it

contains an embedded comment Notice that it ends with a semicolon All of these things are important because they illustrate the following rules for entering SQL statements:

SQL statements may span multiple lines

Line breaks may occur anywhere SQL allows whitespace, but blank lines are not allowed

Comments, delimited by /* */, may be embedded anywhere whitespace is allowed A comment entered this way may span multiple lines

SQL statements must be terminated in one of three ways:

The statement may end with a trailing semicolon

The statement may end with a forward slash character, but the forward slash must be on a line by itself and it must

be in column 1 of that line

The statement may end with a blank line, in which case it will be stored in the SQL buffer rather than be executed

immediately

Pay close attention to the three ways to terminate a SQL statement The reason you have to worry about this at all is because they can span multiple lines, and when you press ENTER for a new line, SQL*Plus needs some way of

knowing whether you are done with the statement or whether you just want to continue it on another line Until you enter a semicolon, a forward slash, or a blank line, SQL*Plus assumes that you are continuing your statement from one line to the next

SQL*Plus 8.1, which ships with Oracle8i, implements a feature allowing you to include blank lines in SQL queries For compatibility reasons, this feature is not enabled by default You can turn it on by issuing the

command SET SQLBLANKLINES ON

I usually recommend terminating SQL statements with semicolons, because I think that's the simplest and cleanest-looking method The SELECT statement above shows a semicolon at the end of the line, but if you forget and hit

ENTER too quickly, you can also put it on the next line by itself For example:

SQL> INSERT INTO project

2 /* all columns */

3 (project_id, project_name, project_budget)

5 VALUES (1006, Mainframe Upgrade, 456789)

6 ;

1 row created

You may also use the forward slash character to terminate a SQL statement, but remember that it must be on a line by itself and must be the first and only character on that line Here is an example:

SQL> UPDATE project

2 SET project_budget = 1000000

3 WHERE project_id = 1006

4 /

1 row updated

You will read more about the forward slash character later in this chapter because it's also used to execute the SQL statement, or PL/SQL block, currently in the SQL buffer

The final option for terminating an SQL statement is to simply press ENTER on a blank line There is a catch to this method, though Here's an example:

SQL> DELETE

2 FROM project

3 WHERE project_id = 1006

4

SQL>

Look carefully at the preceding example Notice that nothing happened! You typed in the DELETE command, pressed ENTER on a blank line, got back another SQL> prompt, but SQL*Plus said nothing about deleting the row that you just asked to delete Why? Because when you terminate an SQL query with a blank line, SQL*Plus stores that command in

an internal buffer but does not execute it You'll read more about this later in this chapter in the section titled The SQL Buffer For now, though, if you haven't entered any other commands after the DELETE statement shown above, just type a forward slash on a line by itself and press ENTER

SQL> /

1 row deleted

Now the DELETE statement has been executed, and the row deleted The forward slash tells SQL*Plus to execute the SQL command most recently entered

If you have been following along with SQL*Plus, and entering the examples while reading this section, you've probably noticed a couple of things First, it's a pain when you make a mistake Second, it's even worse when that mistake is on a previous line If you were using the GUI version of SQL*Plus, you may have even tried to arrow up to correct a

mistyped line Well, don't waste your timeyou can't do that However, SQL*Plus does have some built-inline-editing capabilities, and it can also call the text editor of your choice You'll read about these options in just a bit, after the next section on executing PL/SQL blocks

Working with PL/SQL

PL/SQL is a programming language developed by Oracle as an extension to SQL in order to allow procedural logic to

be implemented at the database level PL/SQL is used to write stored procedures, stored functions, and triggers, and, beginning with Oracle8, to define object types It can also be used to simply write a block of procedural code for the database to execute SQL*Plus was originally one of the

only front-ends that could be used to send PL/SQL code to the database, and even today it is still one of the most widely used

This section explains the mechanics of entering and executing PL/SQL code with SQL*Plus You'll learn what PL/SQL mode is, and you'll learn the differences between entering a PL/SQL block and a SQL query

If you are unfamiliar with PL/SQL, you may want to pick up a copy of Steven Feuerstein and Bill Pribyl's book, Oracle

PL/SQL Programming, second edition (O'Reilly & Associates, 1997) PL/SQL opens up a world of possibilities You'll

want to take advantage of it if you are doing serious work with Oracle

What Is a PL/SQL Block?

The PL/SQL block is the fundamental unit of PL/SQL programming The term block refers to a program unit that

contains some or all of the following elements:

Variable and subprogram declarations

Procedural code, which may include nested PL/SQL blocks

An error handler

Here is an example of a reasonably simple, but complete, PL/SQL block:

DECLARE

X VARCHAAR2(12) := Hello World!;

BEGIN

DBMS_OUTPUT PUT_LINE(X);

EXCEPTION

WHEN OTHERS THEN

DBMS_OUTPUT.PUT_LINE(An error occurred.);

END;

This code contains all the elements of a PL/SQL block, and is one implementation of the traditional Hello World!

program Using SQL*Plus, you can send it to the database for execution

Executing a PL/SQL Block

To execute a PL/SQL block, you type it into SQL*Plus and terminate it with a forward slash The forward slash tells SQL*Plus that you are done entering the block and to send it to the database for execution Here's how it would look to enter and execute the code shown previously:

SQL> DECLARE

2 X VARCHAR2(12) := Hello World!;

3 BEGIN

4 DBMS_OUTPUT.PUT_LINE(X);

5 EXCEPTION

6 WHEN OTHERS THEN