Question

TableA 
id, name
1, abc
2, cde
3, def


TableB
id, TableA_id, topic
1, 1, blah 
2, 1, blah again
3, 2, abcdef 

I want to select all of those records from TableA which dont have any references in TableB. How do I do it in Mysql?

Thanks a lot.

Answer 1

You can use LEFT JOIN and select these records which don’t have matching record in B.

SELECT
  TableA.*
FROM
  TableA
  LEFT JOIN
    TableB 
  ON
    TableB.TableA_id = TableA.id
WHERE
  TableB.id IS NULL