Search notes:

ORA-04091: table … is mutating, trigger/function may not see it

create table tq84_ORA_04091 (
   txt                 varchar2(10)  not null,
   val                 number(5,2)   not null,
   sum_before_ins_upd  number(7,2)
);

create or replace trigger tq84_ORA_04091_trg_before_dml
   before insert or update or delete on tq84_ORA_04091
   for each row  
begin
   select sum(val) into :new.sum_before_ins_upd from tq84_ORA_04091;
end tq84_table_with_trigger_trg;
/

These statements execute without problem:

insert into tq84_ORA_04091 (txt, val) values ('1st ins', 14.18);
insert into tq84_ORA_04091 (txt, val) values ('2nd ins',  5.93);
insert into tq84_ORA_04091 (txt, val) values ('3rd ins', 22.56);

select * from tq84_ORA_04091;

Either of the following statements throws ORA-04091: table …TQ84_ORA_04091 is mutating, trigger/function may not see it:

update      tq84_ORA_04091 set val = 0.01 where txt = '2nd ins';
delete      tq84_ORA_04091                where txt = '2nd ins';

Cleaning up;

drop   table tq84_ORA_04091;

TODO

Mutating table trigger-errors can be avoided with compound DDL triggers.

ORA-04091: table … is mutating, trigger/function may not see it

TODO

See also