Plsql trigger if updating

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.

Constraints are easier to write and less error-prone than triggers that enforce the same rules.

However, triggers can enforce some complex business rules that constraints cannot.

create table Employee( 2 ID VARCHAR2(4 BYTE) NOT NULL, 3 First_Name VARCHAR2(10 BYTE), 4 Last_Name VARCHAR2(10 BYTE), 5 Start_Date DATE, 6 End_Date DATE, 7 Salary Number(8,2), 8 City VARCHAR2(10 BYTE), 9 Description VARCHAR2(15 BYTE) 10 ) 11 / Table created.

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.You can change trigger mode activate/deactivate but you can't explicitly run.Trigger automatically associated with DML statement, when DML statement execute trigger implicitly execute. A trigger defined on a schema fires for each event associated with the owner of the schema (the current user).A trigger defined on a database fires for each event associated with all users. Compound triggers make it easier to program an approach where you want the actions you implement for the various timing points to share common data. When a trigger is fired, the tables referenced in the trigger action might be currently undergoing changes by SQL statements in other users' transactions.4)If you ROLLBACK the transaction before committing to the database, the data inserted to the table is also rolled back.


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