Question

I have the following sql which takes a long time to execute, are there any better way of writing this to improve speed.

Any help is highly appreciable.

Thanks

    SELECT a.KeyField
    FROM Details a,
         Master b
    WHERE a.ForeignKeyField = b.ForeignKeyField
      AND a.KeyField IS NOT NULL
      AND Date BETWEEN 
TO_DATE ('01-01-2011', 'dd-mm-yyyy') AND TO_DATE ('31-12-2011', 'dd-mm-yyyy')
      AND a.KeyField IN
        (SELECT p.KeyField
         FROM Details p,
              Master q
         WHERE q.ForeignKeyField = p.ForeignKeyField
           AND p.KeyField IS NOT NULL
           AND p.KeyField = a.KeyField
           AND q.FKField2 = b.FKField2
         GROUP BY p.KeyField,
                  q.Date HAVING COUNT (DISTINCT q.ForeignKeyField) > 1)
    GROUP BY b.Id,
             b.Name,
             b.ForeignKeyField,
             b.Date,
             a.ForeignKeyField,
             a.SomeOtherField,
             a.KeyField,
             b.EtcEtc

Answer 1

First, you need to learn proper join syntax. My guess is that Oracle is choosing a suboptimal query path because of the correlated subquery. Let’s change it to a join instead:

SELECT a.KeyField
FROM Details a join
 Master b
 on a.ForeignKeyField = b.ForeignKeyField join
 (SELECT p.KeyField, q.Date, q.FKField2
  FROM Details p join
       Master q
       on q.ForeignKeyField = p.ForeignKeyField
  WHERE p.KeyField IS NOT NULL AND
        q.FKField2 = b.FKField2
  GROUP BY p.KeyField, q.Date
  HAVING COUNT (DISTINCT q.ForeignKeyField) > 1
 ) t
 on a.KeyField = t.KeyField and
    b.FKField2 = t.FKField2
WHERE a.KeyField IS NOT NULL AND
  Date BETWEEN TO_DATE ('01-01-2011', 'dd-mm-yyyy') AND TO_DATE ('31-12-2011', 'dd-mm-yyyy') AND
GROUP BY b.Id, b.Name, b.ForeignKeyField, b.Date, a.ForeignKeyField, a.SomeOtherField, a.KeyField, 
     b.EtcEtc

Writing it this way also makes me realize that there is no condition on the Date, although that is used in the subquery. Is this correct?