ORA-04091: table is mutating, trigger/function may

问题:

I have below trigger in which for FIELD_NAME field i want to insert value into FIELD_TRACKING table as 'Deactivation time of KPI in case of Downtime(Select KPI_FREQ_TIME_UNIT FROM KPI_DEFINITION)'. The bracket part in this string value comes from KPI_FREQ_TIME_UNIT field of KPI_DEFINITION table. So below is the trigger i have wrritten for this. The trigger compile without any error. But when i try to change the DNTM_REAC_AFTER_HRS field from the KPI_DEFINITION table then i am getting error ORA-04091: table RATOR_MONITORING_CONFIGURATION.KPI_DEFINITION is mutating, trigger/function may not see it ORA-04088: error during execution of trigger 'RATOR_MONITORING_CONFIGURATION.TRG_TRK_KPI_DEFINITION'.

create or replace TRIGGER RATOR_MONITORING_CONFIGURATION."TRG_TRK_KPI_DEFINITION" AFTER UPDATE ON RATOR_MONITORING_CONFIGURATION.KPI_DEFINITION
      FOR EACH ROW

    IF NOT  :old.DNTM_REAC_AFTER_HRS=:new.DNTM_REAC_AFTER_HRS THEN
        INSERT INTO RATOR_MONITORING_CONFIGURATION.FIELD_TRACKING  (FIELD_TRACKING_ID,TABLE_NAME,TABLE_ID, FIELD_NAME,FIELD_OLD_VALUE,FIELD_NEW_VALUE,USER_ID, TIMESTAMP, FIELD_TRACKING_COMMENTS)
        VALUES (FIELD_TRACKING_SEQ.NEXTVAL,'KPI_DEFINITION',:new.KPI_DEF_ID,'Deactivation time of KPI in case of Downtime'|| '(' || to_char((Select KPI_FREQ_TIME_UNIT FROM KPI_DEFINITION)) || ')',to_char(:old.DNTM_REAC_AFTER_HRS),to_char( :new.DNTM_REAC_AFTER_HRS),:new.LAST_UPDATED_BY,:new.LAST_UPDATED_DATE, decode(:new.KPI_ACTIVE_DOWNTIME,'N','This KPI has been reactivated on end of a downtime.',''));
      END IF;

    END;

回答1:

Trigger cannot read the table (Select KPI_FREQ_TIME_UNIT FROM KPI_DEFINITION), that changes... you can access the value in this way: :new.KPI_FREQ_TIME_UNIT. More info: http://www.dba-oracle.com/t_avoiding_mutating_table_error.htm

In other cases you can try to do it in autonomous transaction:

create or replace TRIGGER RATOR_MONITORING_CONFIGURATION."TRG_TRK_KPI_DEFINITION" 
AFTER UPDATE ON RATOR_MONITORING_CONFIGURATION.KPI_DEFINITION FOR EACH ROW
DECLARE
   PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  -- ...
  COMMIT; -- don't forget it!!!
END;

回答2:

Since you need informations from the table for which you created your trigger for(Select KPI_FREQ_TIME_UNIT FROM KPI_DEFINITION), you can get the KPI_FREQ_TIME_UNIT from the reference :NEW as it represents the new row (:NEW.KPI_FREQ_TIME_UNIT).