There are many restrictions on when youcan use INSTEAD
OF triggers. Refer to your Oracle documentation for a detailed description of the forbidden
scenarios.
Youcan specify a trigger restriction for any trigger. A trigger restriction is a Boolean
expression that circumvents the execution of the trigger if it evaluates to FALSE.
Triggers are defined and stored separately from the tables that use them. Since they
contain logic, they must be written in a language with capabilities beyond those of
SQL, which is designed to access data. Oracle8 and later versions allow youto write
triggers in PL/SQL, the procedural language that has been a part of Oracle since Version
6. Oracle8i and beyond also support Java as a procedural language, so you can
create Java triggers with those versions.
Youcan write a trigger directly in PL/SQL or Java, or a trigger can call an existing
stored procedure written in either language.
Triggers are fired as a result of a SQL statement that affects a row in a particular
table. It??™s possible for the actions of the trigger to modify the data in the table or to
cause changes in other tables that fire their own triggers.
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