Firebird psql updating

24-Oct-2017 00:07

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It is important to keep in mind if no rows are affected by the UPDATE command, the trigger will not execute any code within the trigger.

Statement level triggers will be called once regardless of how many rows are affected by the UPDATE.

Suppose you have a trigger that is made to be called on an UPDATE to a certain table.

Row level triggers would execute once for each row that is affected by the UPDATE.

These trigger types are referred to as "Schema-level triggers". Performing conditional actions in triggers (or testing data following modification) is done through accessing the temporary Inserted and Deleted tables. The following functionality in SQL:2003 was previously not implemented in Postgre SQL: Firebird supports multiple row-level, BEFORE or AFTER, INSERT, UPDATE, DELETE (or any combination thereof) triggers per table, where they are always "in addition to" the default table changes, and the order of the triggers relative to each other can be specified where it would otherwise be ambiguous (POSITION clause.) Triggers may also exist on views, where they are always "instead of" triggers, replacing the default updatable view logic.

(Before version 2.1, triggers on views deemed updatable would run in addition to the default logic.) Firebird does not raise mutating table exceptions (like Oracle), and triggers will by default both nest and recurse as required (SQL Server allows nesting but not recursion, by default.) Firebird's triggers use NEW and OLD context variables (not Inserted and Deleted tables,) and provide UPDATING, INSERTING, and DELETING flags to indicate the current usage of the trigger.

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Triggers can also be used to log historical data, for example to keep track of employees' previous salaries.Syntax for database triggers: IBM DB2 for distributed systems known as DB2 for LUW (LUW means Linux Unix Windows) supports three trigger types: Before trigger, After trigger and Instead of trigger.Both statement level and row level triggers are supported.Here it is important to note that even if the UPDATE command didn’t affect any rows, the code within the trigger will still be executed once.

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Using the BEFORE and AFTER options determine when the trigger is called.Database-level triggers can help enforce multi-table constraints, or emulate materialized views.