Oracle trigger (when A table A is inserted or deleted or modified, the new data can be synchronized to another table B with the same structure)

Create or replace trigger testT
AFTER INSERT OR UPDATE OR DELETE ON
For each row
Declare
-- Local variables here
Begin
IF INSERTING THEN
Insert into B (a, B) VALUES (: NEW. a,: NEW. B );
ELSIF DELETING THEN
Delete from B WHERE a =: OLD.;
ELSE
UPDATE B SET B =: NEW. B WHERE a =: OLD.;
End if;
End testT;

SQL> desc
Name Type Nullable Default Comments
---------------------------------------
A varchar2 (20) y
B varchar2 (20) y

SQL> desc B;
Name type nullable default comments
---------------------------------------
A varchar2 (20) y
B varchar2 (20) y

SQL> insert into a values ('A', 'B ');

1 row inserted

SQL> commit;

Commit complete

SQL> select * from B;

A B
----------------------------------------
A B

SQL> Update a set B = 'C' where a = 'a ';

1 row updated

SQL> commit;

Commit complete

SQL> select * from B;

A B
----------------------------------------
A c

SQL> delete from a where a = 'a ';

1 row deleted

SQL> commit;

Commit complete

SQL> select * from B;

A B
----------------------------------------

SQL>