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When we run SQL statements interactively in SQL*Plus or SQL Developer or another utility, we decide how to react to an error. If a SQL statement fails from a syntax error or from an unexpected data condition such as ORA-01403: no rows found, do we want to proceed and run the next SQL statement, or do we want to simply roll back all work that has been done and exit When executing interactively, we can decide interactively. But what about when we re running a script SQL*Plus provides the WHENEVER command to direct SQL*Plus how to react to failures. WHENEVER is particularly useful when running a script. Table 11-7 describes two variations of the command. Table 11-7. WHENEVER Error-Handling Conditions
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Description
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Triggers whenever a SQL*Plus command like CONNECT, DISCONNECT, SPOOL, HOST, START, or any other command which interacts with the operating system fails. Triggers whenever a SQL statement like SELECT, INSERT, UPDATE, DELETE, CREATE, ALTER, DROP, TRUNCATE, GRANT, REVOKE, or any other SQL command fails.
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Both of the commands in Table 11-7 have two possible directives: EXIT and CONTINUE. Each directive, in turn, implements two further directives describing how to handle an open transaction and (if necessary) what exit status to return to the operating system. Table 11-8 describes the options that you can pass to EXIT and CONTINUE. Table 11-8. WHENEVER Error-Handing Directives
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EXIT [ exit-status | txn-directive ]
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Description
Exit from SQL*Plus with the specified exit status after committing or rolling back the current transaction as directed. Continue executing SQL*Plus after committing, rolling back, or doing nothing.
CONTINUE [ txn-directive ]
WRITING AND AUTOMATING SQL*PLUS SCRIPTS
Exit-status
Can be one of: [ SUCCESS | FAILURE | n | substitution-variable | bindvariable ] where SUCCESS is an operating-system dependent exit status signifying successful completion, FAILURE is an operatingsystem dependent exit status signifying failure, and n is a number value. SQL*Plus substitution variables and SQL*Plus bind variables containing numeric values can also be used as return statuses. SUCCESS is the default.
Txn-directive
Can be one of: [ COMMIT | ROLLBACK | NONE ] where NONE can be used only with the CONTINUE directive. When used with the EXIT directive, COMMIT is the default and when used with the CONTINUE directive, NONE is the default.
So, if a SQL*Plus script contains five UPDATE statements in a row and you want the script to stop executing, roll back any work already performed, and then exit to the operating system with a failure status, your script might look something like that shown in Listing 11-45. Listing 11-45. Error-Handling in a SQL*Plus Script whenever oserror exit failure rollback whenever sqlerror exit failure rollback set echo on feedback on timing on spool update_script update update update update update exit success commit In Listing 11-45, we see the use of the WHENEVER command directing SQL*Plus to exit back to the operating system with a FAILURE exit status, and perform a ROLLBACK as it does so, should any OS commands (such as SPOOL) or SQL commands (such as UPDATE) fail. If all of the commands are successful and we reach the very last line of the script, then we will EXIT back to the operating system with SUCCESS exit status and perform a COMMIT as it does so.
11.7 Exercises
The following exercises allow you to practice using the commands covered in this chapter. See Appendix B for the answers.
WRITING AND AUTOMATING SQL*PLUS SCRIPTS
Look at Listings 11-26 and 11-37. Apart from aesthetics, there is another important reason why the lines surrounding the script headers in those two listings switch from minus signs to equal signs. Obviously, the first two minus signs are mandatory to turn the lines into comments. What would be wrong with using only minus signs Create a SQL*Plus script to create indexes. The script should prompt for a table name and a column name (or list of column names), and then generate the index name according to the following standard: i_<tab-id>_<col-id>. Create a SQL*Plus script to produce an index overview. The script should prompt for a table name, allowing you to specify any leading part of a table name. That is, the script should automatically append a % wildcard to the value entered. Then it should produce a report of all indexes, showing the table name, index name, index type, and number of columns on which the index is based. Create a script that disables all constraints in your schema.
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