Informix Error -741: Trigger for the same event already exists.

Reasons / Common Causes

-741 fires when CREATE TRIGGER defines a trigger for an event a table already has one for — per the official guidance, a table can have only one INSERT trigger and only one DELETE trigger; for UPDATE triggers, multiple are allowed only if each one's triggering column list is mutually exclusive of the others.

1. A second INSERT trigger attempted on a table that already has one, per the official guidance — only one is allowed, full stop.
2. A second DELETE trigger attempted on a table that already has one, per the official guidance — same restriction.
3. A second UPDATE trigger whose triggering column list overlaps with an existing UPDATE trigger's list, per the official guidance — multiple UPDATE triggers are allowed, but only with non-overlapping column lists; the same column can't be named as a triggering column in more than one UPDATE OF (...) clause.

Solutions / Resolution

1. Consolidate logic into the single existing INSERT/DELETE trigger, per the official guidance, rather than attempting a second one — combine both triggers' actions into one trigger's action list.
2. For UPDATE triggers, ensure each trigger's UPDATE OF (...) column list doesn't overlap with any other UPDATE trigger's list, per the official guidance — split the columns across triggers so each column appears in only one.
3. Query systriggers for existing triggers on the table before adding a new one:

   SELECT trigname, event FROM systriggers WHERE tabid =
     (SELECT tabid FROM systables WHERE tabname = 'orders');
   

Examples

A second INSERT trigger

CREATE TRIGGER trg_orders_insert_1 INSERT ON orders ...;
CREATE TRIGGER trg_orders_insert_2 INSERT ON orders ...;
-- -741: orders already has an INSERT trigger

Overlapping UPDATE triggering columns

CREATE TRIGGER trg_status_change UPDATE OF status ON orders ...;
CREATE TRIGGER trg_status_and_ship UPDATE OF status, ship_date ON orders ...;
-- -741: 'status' is a triggering column in both UPDATE triggers

Corrected — non-overlapping UPDATE column lists

CREATE TRIGGER trg_status_change UPDATE OF status ON orders ...;
CREATE TRIGGER trg_ship_change UPDATE OF ship_date ON orders ...;

Diagnostic Checks

1. Query systriggers for the table's existing triggers and their events, and for UPDATE triggers specifically, check the triggering column lists for overlap.

Related Errors / Related Topics

• -742 — "Trigger and cascading-delete referential constraint cannot coexist." A related trigger-restriction error, about delete triggers versus cascading foreign keys rather than multiple triggers on the same event.

Only one INSERT/DELETE trigger per table; multiple UPDATE triggers are fine as long as their triggering column lists don't overlap.