Question

I have a one to many relationship between tables A (columns ID and DESC) and B (columns FK_ID, CODE). ID-> FK_ID.

I’m curious to find the most efficient SQL to select all rows in A where there is a code in B named ‘C1’ but there is NOT a code in B named ‘N1’.

Any help appreciated.

Answer 1

Using EXISTS and NOT EXISTS would give the best performance

SELECT tableA.*
FROM tableA
WHERE
  EXISTS(
    SELECT NULL
    FROM TableB 
    WHERE tableA.ID = TableB.FK_ID AND TableB.Code = 'C1')
  AND NOT EXISTS(
    SELECT NULL
    FROM TableB 
    WHERE tableA.ID = TableB.FK_ID AND TableB.Code = 'N1')