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 Data Manipulation (DML) StatementsBuilt-in Scalar Functions 

OLD and NEW Context Variables

For DML triggers, the Firebird engine provides access to sets of OLD and NEW context variables (or, “records”).Each is a record of the values of the entire row: one for the values as they are before the data-changing event (the BEFORE phase) and one for the values as they will be after the event (the AFTER phase).They are referenced in statements using the form NEW.column_name and OLD.column_name, respectively.The column_name can be any column in the table’s definition, not just those that are being updated.

The NEW and OLD variables are subject to some rules:

  • In all triggers, OLD is read-only

  • In BEFORE UPDATE and BEFORE INSERT code, the NEW value is read/write, unless it is a COMPUTED BY column

  • In INSERT triggers, references to OLD are invalid and will throw an exception

  • In DELETE triggers, references to NEW are invalid and will throw an exception

  • In all AFTER trigger code, NEW is read-only

Database Triggers

A trigger associated with a database or transaction event can be defined for the following events:

Connecting to a database

ON CONNECT

Before the trigger is executed, a transaction is automatically started with the default isolation level (snapshot (concurrency), write, wait)

Disconnecting from a database

ON DISCONNECT

Before the trigger is executed, a transaction is automatically started with the default isolation level (snapshot (concurrency), write, wait)

When a transaction is started

ON TRANSACTION START

The trigger is executed in the transaction context of the started transaction (immediately after start)

When a transaction is committed

ON TRANSACTION COMMIT

The trigger is executed in the transaction context of the committing transaction (immediately before commit)

When a transaction is cancelled

ON TRANSACTION ROLLBACK

The trigger is executed in the transaction context of the rolling back transaction (immediately before roll back)