Oracle SQL Plus The Definitive Guide- P6 pptx

< previous page page_27 next page > Page 27 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. < previous page page_27 next page > < previous page page_28 next page > Page 28 Help 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. < previous page page_28 next page > < previous page page_29 next page > Page 29 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. < previous page page_29 next page > < previous page page_30 next page > Page 30 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 < previous page page_30 next page > < previous page page_31 next page > Page 31 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 pass- < previous page page_31 next page > < previous page page_32 next page > Page 32 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 < previous page page_32 next page > < previous page page_33 next page > Page 33 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. < previous page page_33 next page > < previous page page_34 next page > Page 34 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. < previous page page_34 next page > < previous page page_35 next page > Page 35 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 < previous page page_35 next page > < previous page page_36 next page > Page 36 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 < previous page page_36 next page > . help on SQL statements, SQL* Plus commands, and PL /SQL commands. SQL* Plus 8.1, released with Oracle8 i, provides help only on SQL* Plus commands. This is because there wasn't time for Oracle. 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. 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