Question

我有这个问题，我似乎无法完美。任何帮助将不胜感激。使用SQL Server 2008 R2。

即使没有该社区的记录，我也会尝试显示结果中的所有社区。

SELECT COALESCE(SUM(D.FulfillmentAmt),0) as Approved, DB.Budget, DC.CommunityName 
FROM Donations D
LEFT JOIN DCommunity DC ON D.Market = DC.CID
LEFT JOIN DBudget DB ON D.Market = DB.Community
WHERE D.StatusId = '1' AND DB.[Year] = year(getdate())
GROUP BY DC.CommunityName, DB.Budget
ORDER BY DC.CommunityName

目前显示以下结果：

Approved | Budget | CommunityName
10       | 2000   | City1
2400     | 3000   | City2
2358     | 5000   | City3
1855     | 2000   | City5
2200     | 3000   | City6
5600     | 7000   | City8

正如您所看到的那样，它缺少City4和City7，因为dbo.Donations表中没有针对这些城市的记录。即使他们没有记录，我仍然希望这两个人显示批准金额为0。

Answer 1

由于你想要所有社区，作为一种风格，我总是把它作为我加入的第一张桌子（我更容易思考）。然后，您需要将WHERE条件适当地移动到JOIN子句中，因为将它们保留在WHERE中会强制它像INNER JOIN一样运行。此外，DBudget上的连接需要更新以返回DCommunity表。

SELECT COALESCE(SUM(D.FulfillmentAmt),0) as Approved, DB.Budget, DC.CommunityName 
FROM DCommunity DC
LEFT JOIN DBudget DB ON DC.CID  = DB.Community AND DB.[Year] = year(getdate())
LEFT JOIN Donations D ON D.Market = DC.CID AND D.StatusId = '1'
GROUP BY DC.CommunityName, DB.Budget
ORDER BY DC.CommunityName

Answer 2

然后使用left join启动DCommunity，如果这是您要保留的内容。此外，您需要将一些条件移至on子句，因此left join不会成为inner加入次数：

SELECT COALESCE(SUM(D.FulfillmentAmt), 0) as Approved, DB.Budget, DC.CommunityName 
FROM DCommunity DC LEFT JOIN
     Donations D
     ON D.Market = DC.CID LEFT JOIN
     DBudget DB
     ON D.Market = DB.Community AND
        D.StatusId = '1' AND
        DB.[Year] = year(getdate())
GROUP BY DC.CommunityName, DB.Budget
ORDER BY DC.CommunityName;

Answer 3

将条件从WHERE移至ON，以获得真实的LEFT JOIN。（否则你会得到一个常规的INNER JOIN ...）

SELECT COALESCE(SUM(D.FulfillmentAmt),0) as Approved,
       DB.Budget,
       DC.CommunityName 
FROM DCommunity DC 
  LEFT JOIN Donations D ON D.Market = DC.CID AND D.StatusId = '1'
  LEFT JOIN DBudget DB ON D.Market = DB.Community AND DB.[Year] = year(getdate())
GROUP BY DC.CommunityName, DB.Budget
ORDER BY DC.CommunityName

即使没有要显示的记录，也显示0

3 个答案: