Sql server 2008 寻找更好的Sql查询

我需要使用表

@tblchildata

的

MAX ChildDateTime

和

IsLast

=1更新

@tblData

表的

LastDateTime

列

Declare @tblData Table(DId Int, TypeId Int, LastDateTime DateTime)
Insert Into @tblData Values(1, 1, Null), (2, 2, Null), (3, 2, Null)

Declare @tblChildData Table(CId Int, DId Int, ChildDateTime DateTime, IsLast Bit)
Insert Into @tblChildData Values (10, 1, '2016-09-20 07:47:03.000', Null)
    , (11, 2, '2016-09-20 08:47:03.000', Null)
    , (12, 2, '2016-09-20 09:32:03.000', 1)
    , (13, 2, '2016-09-20 10:47:03.000', Null)
    , (14, 2, '2016-09-20 11:32:03.000', 1)
    , (15, 1, '2016-09-20 06:47:03.000', Null)

我能够更新以下查询，但寻找更好的查询。谢谢

UPDATE UQ
SET UQ.LastDateTime = (
    SELECT MAX(D.ChildDateTime)
    FROM @tblData C
    JOIN @tblChildData D ON C.DId = D.DId
        AND C.TypeId = 2
        AND D.IsLast = 1
)
FROM @tblData UQ
JOIN @tblChildData PD ON UQ.DId = PD.DId
    AND UQ.TypeId = 2
    AND PD.IsLast = 1

SELECT * FROM @tblData

---

您可以尝试如下更新：

UPDATE t
SET t.lastDateTime = (SELECT
  MAX(childDatetime)
FROM @tblChildData
WHERE did = t.did
AND IsLast = 1)
FROM @tblData t

不确定您为什么在下面再次加入childdata。检查输出与预期输出。显然，它的性能会更好，因为它不会再次加入另一个表。下面是您的查询与执行计划之间的比较

我的更新脚本

您的更新脚本

---

您可以尝试如下更新：

UPDATE t
SET t.lastDateTime = (SELECT
  MAX(childDatetime)
FROM @tblChildData
WHERE did = t.did
AND IsLast = 1)
FROM @tblData t

不确定您为什么在下面再次加入childdata。检查输出与预期输出。显然，它的性能会更好，因为它不会再次加入另一个表。下面是您的查询与执行计划之间的比较

我的更新脚本

您的更新脚本

你可以试试这个

UPDATE UQ SET UQ.LastDateTime = (
SELECT MAX(D.ChildDateTime)
FROM @tblChildData D where D.DId=UQ.DId
    AND UQ.TypeId = 2
    AND D.IsLast = 1) FROM @tblData UQ where UQ.TypeId = 2

你可以试试这个

UPDATE UQ SET UQ.LastDateTime = (
SELECT MAX(D.ChildDateTime)
FROM @tblChildData D where D.DId=UQ.DId
    AND UQ.TypeId = 2
    AND D.IsLast = 1) FROM @tblData UQ where UQ.TypeId = 2

---

谢谢你更好的编辑谢谢你更好的编辑