需要优化这个 Oracle SQL 查询

Question

My query takes too much time to fetch data. Each table (ap1, ap2, ap4) has 1626 records. Please help me to optimize the query

SELECT *
FROM ap1 w1,
     ap2 w2, 
     ap4 w4
WHERE w4.first_name = '2'
  AND w4.id = '303'
  AND w4.reference like '%AXS%'
  AND w1.first_name = w4.first_name
  AND w2.first_name = w1.first_name
  AND w1.id = w4.id
  AND w2.id = w4.id
  AND w1.number = w4.number
  AND w2.number = w4.number;

Thanks

Answer 1

The proper way to write the query is:

SELECT *
FROM ap1 w1 JOIN
     ap2 w2
     ON w2.first_name = w1.first_name AND
        w2.id = w4.id JOIN
     ap4 w4
     ON w1.first_name = w4.first_name AND
        w1.id = w4.id AND
        w1.number = w4.number
WHERE w4.first_name = '2' AND
      w4.id = '303' AND
      w4.reference like '%AXS%';

This makes it clear that you want an index on w4(id, first_name, reference, id, number) . And then on w1(id, first_name, number) and on w2(id, first_name)`.

However, this assumes that the join conditions are correct. If you query is performing so poorly on small numbers of rows, then they might be wrong. I would suggest that you build up the query one table at a time to be sure the logic is correct.