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WRITING AND AUTOMATING SQL*PLUS SCRIPTS
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SQL> select * from employees where empno = 7566; SQL> select * from employees where empno = 7900; These two SQL statements are obviously different, and the Oracle DBMS will also treat them as such. The optimizer will optimize them separately, and they will occupy their own memory structures (cursors). This approach can easily flood your internal memory, and it also forces the optimizer to produce execution plans over and over again. A much better approach would be to use a bind variable in the SQL command, instead of the literal employee number, and to provide values for the bind variable separately. In other words, all SQL commands coming from the application look like the following: SQL> select * from employees where empno = :x; Now, the Oracle DBMS is able to use cursor sharing, the optimizer can produce a single execution plan, and the SQL command can be executed many times for different values of the bind variable. SQL*Plus offers support for bind variables with the VARIABLE and PRINTcommands. You will also use the SQL*Plus EXECUTE command, allowing you to execute a single PL/SQL statement.
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You can declare bind variables with the SQL*Plus VARIABLE command, and you can display bind variable values with the SQL*Plus PRINT command. Because SQL doesn t support any syntax to assign values to bind variables, we use the SQL*Plus EXECUTE command to execute a single PL/SQL command from SQL*Plus. Listing 11-16 shows examples of using these commands. Listing 11-16. Declaring Bind Variables and Assigning Values SQL> variable x number SQL> variable y varchar2(8) SQL> execute :x := 7566 PL/SQL procedure successfully completed. SQL> execute :y := 'ADMIN' PL/SQL procedure successfully completed. SQL> print x y X -----7566 Y -------------------------------ADMIN SQL> variable variable x datatype NUMBER variable y
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datatype SQL>
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VARCHAR2(8)
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As you can see, we have created two variables, we have assigned values to them, and we can display those values. Note that := is the assignment operator in PL/SQL.
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Now let s see whether we can retrieve the same two employees (7566 and 7900) using a bind variable. See Listing 11-17. Listing 11-17. Using Bind Variables in SQL Commands SQL> select * from employees where empno = :x; EMPNO ENAME INIT JOB MGR BDATE MSAL COMM DEPTNO ------ -------- ----- -------- ----- ----------- ------ ----- -----7566 JONES JM MANAGER 7839 02-APR-1967 2975 20 SQL> execute :x := 7900 PL/SQL procedure successfully completed. SQL> run 1* select * from employees where empno = :x EMPNO ENAME INIT JOB MGR BDATE MSAL COMM DEPTNO ------ -------- ----- -------- ----- ----------- ------ ----- -----7900 JONES R ADMIN 7698 03-DEC-1969 800 30 SQL> Because EXECUTE is a SQL*Plus command, which means it is not stored in the SQL buffer, you can assign a new value and re-execute the query from the SQL buffer with the RUN command. If you want to see some evidence of the behavior of the Oracle DBMS, take a look at Listing 11-18. Listing 11-18. Querying V$SQLAREA to See the Differences SQL> select executions, sql_text 2 from v$sqlarea 3 where sql_text like 'select * from employees %'; EXECUTIONS ---------2 1 1 SQL> SQL_TEXT -----------------------------------------select * from employees where empno = :x select * from employees where empno = 7566 select * from employees where empno = 7900
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WRITING AND AUTOMATING SQL*PLUS SCRIPTS
For more details about bind variables, refer to PL/SQL User s Guide and Reference.
11.3 SQL*Plus Scripts
In 2, you learned that you can save SQL commands with the SQL*Plus SAVE command. Until now, we have written only single SQL commands from the SQL buffer to a file. However, you can also create files with multiple SQL commands, optionally intermixed with SQL*Plus commands. This type of file is referred to as a SQL*Plus script.
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