Oracle strongly recommends that you use triggers to constrain data input only in these situations: created on a table or editioning view can fire at one, some, or all of the preceding timing points.

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A constraint can apply either to new data only (like a trigger) or to both new and existing data.

Constraint behavior depends on constraint state, as explained in .

While a trigger is , which determines whether the trigger fires before or after the triggering statement runs and whether it fires for each row that the triggering statement affects. If the trigger is created on a schema or the database, then the triggering event is composed of either DDL or database operation statements, and the trigger is called a )".

By default, a trigger is created in the enabled state. When a trigger fires, tables that the trigger references might be undergoing changes made by SQL statements in other users' transactions.

Asked: November 26, 2006 - pm UTC Answered by: Tom Kyte - Last updated: November 14, 2012 - pm UTC Category: Database - Version: 9.2.0.7 Viewed 10K times! The problem with one I defined is for every update/delete (even that update does not involve these two columns) it is checking whether the column has changed or not.

This question is Hi Tom We got a de-normalized table with around 150 columns and around 50 millions rows. Dont you think we need such feature in Oracle, if not already available.SQL statements running in triggers follow the same rules that standalone SQL statements do.Specifically: How Triggers and Constraints Differ Both triggers and constraints can constrain data input, but they differ significantly. For example, a trigger can prevent a DML statement from inserting a values that were inserted into the column before the trigger was defined or while the trigger was disabled.Like a stored procedure, a trigger is a named PL/SQL unit that is stored in the database and can be invoked repeatedly.Unlike a stored procedure, you can enable and disable a trigger, but you cannot explicitly invoke it.CREATE or REPLACE TRIGGER emp_after_update AFTER UPDATE OF empid ON emp FOR EACH ROW DECLARE BEGIN update emp_backup set empid = :new.empid where empid = :old.empid; DBMS_OUTPUT.