How do I create this trigger? - sql

Question

I have two tables: table1 and table2. I have a trigger in table1 that inserts the current row into table2 based on some conditions. If the row gets inserted into table2, I want to delete that row from table1. Now in Oracle, it seems we cannot delete the current row from the trigger in table1 itself.

Answer 1

A row level trigger on a table can manipulate the data of the updated rows. It cannot perform additional dml on the table itself (select, insert, delete).
A possible solution is to create a view on table1 with an INSTEAD OF trigger that deletes from table1 and perform all insert/update/delete statements on the view instead of the table
Example: when test_table.name is updated to 'KOEN', then row itself will be deleted. This example shows just an ON UPDATE trigger but it can be done for INSERT/UPDATE/DELETE:
CREATE TABLE test_table (
id NUMBER
GENERATED BY DEFAULT ON NULL AS IDENTITY
CONSTRAINT test_table_id_pk PRIMARY KEY,
name VARCHAR2(100 CHAR)
);
CREATE VIEW test_table_v AS
SELECT
id,
name
FROM
test_table;
CREATE OR REPLACE TRIGGER test_table_v_bu
INSTEAD OF UPDATE ON test_table_v
FOR EACH ROW
DECLARE
BEGIN
-- do your stuff on the other table.
IF :NEW.NAME = 'KOEN' THEN
DELETE FROM test_table WHERE id = :NEW.ID;
END IF;
END;
/
koen>INSERT INTO test_table ( name ) VALUES ( 'JIM' );
1 row inserted.
koen>select * from test_table;
ID NAME
_____ _______
3 JIM
koen>update test_table_v set name= 'KOEN';
1 row updated.
stapp_dev--SAMPLEAPPS>select * from test_table;
no rows selected
koen>