Question

I have tow tables in my MySQL database – one with flights and one with tickets. Relation between flight and ticket is one to many. I want to delete all flights for which there are no tickets or they are canceled. How to do this with one SQL statement.

What I have now:

M('Db')->exec('
    DELETE
        f
    FROM
        flight f
    LEFT JOIN
        ticket p

    ON
         f.session_id = p.flight_session_id AND 
         f.id = p.flight_id

    WHERE
         f.cdate < ? AND
         ( p.is_canceled =1 OR p.id IS NULL ) 
    ', $this->getSweepTime());

This statement does not take in account flights for which exist both canceled and not canceled tickets. So I should correct it, but I have no idea how to do this in one statement.

Answer 1

DELETE FROM Flight f
WHERE  f.cdate < ?
       AND
       (NOT EXISTS (SELECT 1
                    FROM   ticket t
                    WHERE  f.session_id = p.flight_session_id
                           AND f.id = p.flight_id) OR EXISTS
        (SELECT 1
         FROM   ticket t
         WHERE  f.session_id = t.flight_session_id
                AND f.id = t.flight_id HAVING
          SUM(Canceled) - COUNT(*) = 0))