tsql 2012隐式连接8个表
tsql 2012隐式连接8个表
提问于 2014-04-25 06:05:59
我正在尝试理解以下带有隐式连接的t-sql 2012目前是如何在生产中执行的：
SELECT distinct Cyear
FROM dbo.Individual INNER JOIN
dbo.Course INNER JOIN
dbo.CalendarYear ON dbo.Course.CalendarYearID = dbo.CalendarYear.CalendarYearID
AND CalendarYear.endYear >= (SELECT DISTINCT A.endYear FROM CalendarYear A WHERE
A.active = 1)
INNER JOIN
dbo.Cust ON dbo.CalendarYear.CustID = dbo.Cust.CustID INNER JOIN
dbo.BridgeCust ON dbo.Course.CourseID = dbo.BridgeCust.CourseID ON
dbo.Individual.StudID = dbo.BridgeCust.StudID INNER JOIN
dbo.User INNER JOIN
dbo.BridgeUser ON dbo.User.UserID = dbo.BridgeUser.UserID
ON dbo.BridgeCust.CourseID = dbo.BridgeUser.CourseID与dbo.Course表的dbo.Individual没有直接连接。第一次连接dbo.Individual是使用BridgeCust表。仅为该表的键加上dbo.Individual和dbo.Course表的键设置bridgeCust表。
因此，你能向我解释一下隐式连接是如何设置的吗？
您是否可以编写sql来向我展示设置为真正显式执行的sql？
回答 1
Stack Overflow用户
发布于 2014-11-06 19:58:09
这可能就是正在发生的事情。
SELECT DISTINCT Cyear
FROM dbo.Individual
INNER JOIN dbo.Course
INNER JOIN dbo.CalendarYear
ON dbo.Course.CalendarYearID = dbo.CalendarYear.CalendarYearID
AND CalendarYear.endYear >= (
SELECT DISTINCT
A.endYear
FROM CalendarYear AS A
WHERE A.active = 1)
INNER JOIN dbo.Cust
ON dbo.CalendarYear.CustID = dbo.Cust.CustID
INNER JOIN dbo.BridgeCust
ON dbo.Course.CourseID = dbo.BridgeCust.CourseID
ON dbo.Individual.StudID = dbo.BridgeCust.StudID
INNER JOIN dbo.[User]
INNER JOIN dbo.BridgeUser
ON dbo.[User].UserID = dbo.BridgeUser.UserID
ON dbo.BridgeCust.CourseID = dbo.BridgeUser.CourseID;或者像下面这样重写它，它可能会更清楚。
SELECT DISTINCT Cyear
FROM dbo.Individual
INNER JOIN (SELECT dbo.BridgeCust.StudID,dbo.BridgeCust.CourseID FROM dbo.Course
INNER JOIN dbo.CalendarYear
ON dbo.Course.CalendarYearID = dbo.CalendarYear.CalendarYearID
AND CalendarYear.endYear >= (
SELECT DISTINCT A.endYear
FROM CalendarYear AS A
WHERE A.active = 1)
INNER JOIN dbo.Cust
ON dbo.CalendarYear.CustID = dbo.Cust.CustID
INNER JOIN dbo.BridgeCust
ON dbo.Course.CourseID = dbo.BridgeCust.CourseID) F1
ON dbo.Individual.StudID = F1.StudID
INNER JOIN (SELECT dbo.BridgeUser.UserID, dbo.BridgeUser.CourseID FROM dbo.[User]
INNER JOIN dbo.BridgeUser
ON dbo.[User].UserID = dbo.BridgeUser.UserID) F2
ON F2.CourseID = F1.CourseID;页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/23280738
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