How Modifying a Column Affects Triggers

If you modify a column that appears in the triggering column list of an UPDATE trigger, the trigger is unchanged.

When you modify a column in a table, the triggers based on that table remain unchanged, but the column modification might invalidate the trigger.

CREATE TABLE tab1 (i1 INT, i2 INT, i3 INT);
CREATE TABLE tab2 (i4 INT, i5 INT);
CREATE TRIGGER col1trig UPDATE OF i2 ON tab1 
   BEFORE(INSERT INTO tab2 VALUES(1,1)); 
ALTER TABLE tab2 MODIFY i4 CHAR;

After the ALTER TABLE statement, column i4 accepts only character values. Because character columns accept only values enclosed in quotation marks, the action clause of the col1trig trigger is invalidated.

If a trigger is invalidated when you modify the underlying table, drop and then re-create the trigger.