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Editorial Team
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Asked: 2026-05-27T07:56:26+00:00

I have a query which uses a self join on 2 tables to return

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I have a query which uses a self join on 2 tables to return a single row of results. The problem I have is that if seat1 is empty, I don’t get anything returned.

SELECT seat1.seat_type_id
     , seat1.seat_type_qty
     , seat2.seat_type_id
     , seat2.seat_type_qty
  FROM jos_sv_apptpro2_requests AS R 
  LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 ON R.id_requests = seat1.request_id 
  LEFT JOIN jos_sv_apptpro2_seat_counts AS seat2 ON R.id_requests = seat2.request_id
 WHERE (seat1.seat_type_id = 6 AND seat2.seat_type_id = 7)
   AND R.id_requests = 8703
   AND R.resource = 3

This should return:

seat_type_id 6
seat_type_qty 0 <= this is the empty row
seat_type_id1 7
seat_type_qty 1
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1 Answer

  1. Editorial Team
    WHERE seat1.seat_type_id = 6 AND seat2.seat_type_id = 7

    is what removes all rows with NULL values. You should move those condition to the JOIN criteria so that the RDBMS does what you are expecting:

    LEFT JOIN jos_sv_apptpro2_seat_counts AS seat1 ON R.id_requests = seat1.request_id 
                                              AND seat1.seat_type_id = 6
LEFT JOIN jos_sv_apptpro2_seat_counts AS seat2 ON R.id_requests = seat2.request_id
                                              AND seat2.seat_type_id = 7
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