java - 我的查询需要很长时间才能完成查找列值差异为另一列最大分组的行对

Question

比如说，我有一张这样的 table :

我想找到每次 session 中性能差异最大的一对中心，如下所示:

我有以下查询，

select 
    t1.session,
    t1.center center1,
    t2.center center2,
    t1.performance - t2.performance performance
from mytable t1
inner join mytable t2 on t1.session = t2.session
where t1.performance - t2.performance = (
    select max(t11.performance - t22.performance)
    from mytable t11
    inner join mytable t22 on t11.session = t22.session
    where t11.session = t1.session
)

它可以工作，但对于 20 列和 200 行的表来说需要很长时间，几分钟。 如何修改查询以更快地实现相同的输出？

Answer 1

select 
        t1.session,
        t1.center center1,
        t2.center center2,
        t1.performance - t2.performance performance
    from mytable t1
    inner join mytable t2 
       on t1.session = t2.session
    WHERE t1.performance = (SELECT MAX(performance) 
                            FROM mytable t3 WHERE t3.session = t1.session)
      AND t2.performance = (SELECT MIN(performance) 
                            FROM mytable t3 WHERE t3.session = t2.session)

     // Im thinking this will solve the border case when performance is a tie 
     // and difference 0 will return 2 rows

     AND (CASE WHEN t1.performance = t2.performance 
               THEN CASE WHEN t1.center < t2.center
                         THEN 1
                         ELSE 0
                    END
               ELSE 1
          END) = 1

只要您有关于性能和 session 的索引就应该没问题。