SQL - if record exists in tableA, then insert into tableB

Question

I'm using a mysql database, and I'm trying to insert a record into tableB if the product code already exists in tableA.

I think a CASE statement would work, but I can't find any further help on the web. Here is what I have so far:

CASE (SELECT COUNT(*) FROM tableA WHERE tableA.item_code = '$pcode') > 1 
THEN INSERT INTO tableB(item_id, serial_number, used) 
VALUES ('$iid','$sns','$used') END

Any help greatly appreciated. Cheers

Answer 1

You just need to write a regular old insert statement:

insert into tableB(item_id, serial_number, used)
select '$iid', '$sns', '$used'
where exists (select 1 from tableA where item_code = '$pcode')

Answer 2

insert into tableB(item_id, serial_number, used)
select item_id, '$sns', 1
from tableA where item_code = '$pcode'

Answer 3

Here:

INSERT INTO tableB
            (productcode)
SELECT productcode
FROM   tableC c
WHERE  EXISTS (SELECT productcode
               FROM   tableA a
               WHERE  a.productcode = c.productcode) 

Answer 4

or if you put a foreign key on the item_codes you could just insert the record in the usual way

INSERT INTO tableB(item_id, serial_number, used)  VALUES ('$iid','$sns','$used')

and catch the exception if it happens...

see: Handling foreign key exceptions in PHP

the benifit of this approach is that the database is automatically enforcing the rule for you.