Oracle 18c

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select * from V$VERSION;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


create table t
( a int,
  b int,
  c int,
  primary key (a) 
) ;
insert into t (a, b, c) values (1, 2, 3) ;
1 rows affected

insert into t (a, b, c) values (2, 5, 7) ;
1 rows affected

insert into t (a, b, c) values (3, 4, 7) ;
1 rows affected

CREATE OR REPLACE TRIGGER testing_mutating_table 
   BEFORE UPDATE 
   ON t 
   FOR EACH ROW 
BEGIN 
    IF :NEW.b <> :OLD.b OR :NEW.a <> :OLD.a THEN
         :NEW.c := :NEW.a + :NEW.b   ;
    END IF ;
END ; /
update t 
set b = 20 
where a = 3 ;
1 rows affected

select * from t ;


A
B
C


1
2
3

2
5
7

3
20
23