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Database triggers
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Author:
Adriano dos Santos Fernandes <adrianosf@uol.com.br>

Syntax:
<database-trigger> ::=
{CREATE | RECREATE | CREATE OR ALTER}
TRIGGER <name>
[ACTIVE | INACTIVE]
ON <event>
[POSITION <n>]
AS
BEGIN
...
END

<event> ::=
CONNECT
| DISCONNECT
| TRANSACTION START
| TRANSACTION COMMIT
| TRANSACTION ROLLBACK

Syntax rules:
1) Database triggers type can't be changed.

Utilities support:
New parameters were added to GBAK, ISQL and NBACKUP to not run database triggers.
These parameters could only be used by database owner and SYSDBA:
GBAK -nodbtriggers
ISQL -nodbtriggers
NBACKUP -T

Permissions:
Only database owner and SYSDBA can do database triggers DDL.

Events descriptions:

- CONNECT
Database connection established
A transaction is started
Triggers are fired - uncaught exceptions rollback the transaction,
disconnect the attachment and are returned to the client
The transaction is committed

- DISCONNECT
A transaction is started
Triggers are fired - uncaught exceptions rollback the transaction,
disconnect the attachment and are swallowed
The transaction is committed
The attachment is disconnected

- TRANSACTION START
Triggers are fired in the newly user created transaction - uncaught
exceptions are returned to the client and the transaction is rolled-back.

- TRANSACTION COMMIT
Triggers are fired in the committing transaction - uncaught exceptions
rollback the triggers savepoint, the commit command is aborted and the
exception is returned to the client.
Note: for two-phase transactions the triggers are fired in "prepare"
and not in commit.

- TRANSACTION ROLLBACK
Triggers are fired in the rolling-back transaction - changes done will
be rolled-back togheter with the transaction and exceptions are swallowed