Join With Union in sql 查询查杀性能

Question

有什么方法可以改进下面的查询吗？

下面的查询给出了正确的结果，但会降低性能。

Answer 1

也许是这样的？

Select 
  ID,
  max(case when MYDATE = '20160105 10:00:00' then PRICE else 0 end),
  max(case when MYDATE = '20140805 10:00:00' then PRICE else 0 end),
  max(case when MYDATE = '20170215 10:00:00' then PRICE else 0 end)
FROM
(
  select ID, PRICE FROM TABLE1 WHERE MYDATE in ('20160105 10:00:00', '20140805 10:00:00', '20170215 10:00:00')
  UNION ALL
  SELECT ID, PRICE FROM TABLE2 WHERE MYDATE in ('20160105 10:00:00', '20140805 10:00:00', '20170215 10:00:00')
) A
group by ID

如果你能提供任何例子，猜测会更容易...

Answer 2

您可以避免 ( ) ，使用 A.ID 进行连接，这可能会对性能产生一些好处

Select A.ID, A.[2016 Price], B.[2014 Price], C.[2017 Price]
FROM

  (
  select ID, PRICE [2016 Price] FROM TABLE1 WHERE MYDATE = 2016-01-05 10:00:00
  UNION
  SELECT ID, PRICE FROM TABLE2 WHERE MYDATE = 2016-01-05 10:00:00
  ) A 

INNER JOIN

  (
  select ID, PRICE [2014 Price] FROM TABLE1 WHERE MYDATE = 2014-08-05 10:00:00
  UNION
  SELECT ID, PRICE FROM TABLE2 WHERE MYDATE = 2014-08-05 10:00:00
  ) B ON A.ID =B.ID

INNER JOIN

  (
  select ID, PRICE [2017 Price] FROM TABLE1 WHERE MYDATE = 2017-02-15 10:00:00
  UNION
  SELECT ID, PRICE FROM TABLE2 WHERE MYDATE = 2017-02-15 10:00:00
  )  ON A.ID =C.ID

Join With Union in sql 查询查杀性能

Join With Union in sql query killing performance

sql

sql-server

performance

query-performance