How to Delete Rows That do not Exist in Another Table
select a.orderid from web.orderHeader a
WHERE web.orderHeader.orderid NOT IN (SELECT f.orderid
FROM web.orderdetail f)
Using NOT IN:
DELETE FROM orderHeader WHERE orderid NOT IN (SELECT f.orderid FROM orderdetail f)
Using NOT EXISTS:
DELETE FROM orderHeader WHERE NOT EXISTS(SELECT NULL FROM orderdetail f
WHERE f.id = fileid)