Question

I can’t seem to get the syntax right. I’m looking to check a table for a value before allowing another record to be inserted.

Something like this:

IF EXISTS (SELECT * FROM rooms WHERE id = 1)
THEN
INSERT INTO other_table (room_id) VALUES (1)
END IF

I just want to make sure a particular record exists before it’s allowed to be entered in another table… To go even further, I’d actually like to make sure a couple things exist…

IF EXISTS (SELECT * FROM rooms WHERE id = 1) AND (SELECT * FROM guests WHERE guest_id = 10)
THEN
INSERT INTO other_table (room_id,guest_id) VALUES (1,10)
END IF

I’m not up on transactions yet, or stored procedures, so if I need to learn all of that first, I’m going to be sad.

Answer 1

You can use INSERT INTO ... SELECT :

INSERT INTO other_table (room_id) 
SELECT 1 FROM rooms WHERE id  =1 GROUP BY id

(GROUP BY just to make sure the subquery returns no more than 1 row; if rooms.id is unique, you don’t need it.

For multiple tables:

INSERT INTO other_table (room_id,guest_id) 
SELECT 1, 
10
FROM rooms WHERE id = 1 and exists (SELECT 1 FROM guests WHERE guest_id = 10) LIMIT 1;