About Trigger Compilation and Dependencies

Running a CREATE TRIGGER statement compiles the trigger being created. If this compilation causes an error, the CREATE TRIGGER statement fails. To see the compilation errors, run this statement:

SELECT * FROM USER_ERRORS WHERE TYPE = 'TRIGGER';

Compiled triggers depend on the schema objects on which they are defined. For example, NEW_EVALUATION_TRIGGER depends on the EVALUATIONS table:

CREATE OR REPLACE
TRIGGER NEW_EVALUATION_TRIGGER
BEFORE INSERT ON EVALUATIONS
FOR EACH ROW
BEGIN
  :NEW.evaluation_id := evaluations_seq.NEXTVAL;
END;

To see the schema objects on which triggers depend, run this statement:

SELECT * FROM ALL_DEPENDENCIES WHERE TYPE = 'TRIGGER';

If an object on which a trigger depends is dropped, or changed such that there is a mismatch between the trigger and the object, then the trigger is invalidated. The next time the trigger is invoked, it is recompiled. To recompile a trigger immediately, run the ALTER TRIGGER statement with the COMPILE clause. For example:

ALTER TRIGGER NEW_EVALUATION_TRIGGER COMPILE;