SQL WHERE子句问题

Question

我遇到的问题似乎来自我的where子句和硬编码。 我有两个表，一个是ID，另一个是ID和ID。

所以我的代码看起来有点像这样：

SELECT AVG(CAST(c.Score AS DEC(10,2))) AS avgTestC, 
     AVG(CAST(d.Score AS DEC(10,2))) AS avgTestD, 
     AVG(CAST(e.Score AS DEC(10,2))) AS avgTestE, 
     AVG(CAST(f.Score AS DEC(10,2))) AS avgTestF, 
     COUNT(DISTINCT c.ID) AS CountC, 
     COUNT(DISTINCT d.ID) AS CountD, 
     COUNT(DISTINCT e.ID) AS CountE, 
     COUNT(DISTINCT f.ID) AS CountF 
FROM tblWithIds a, 
    JOIN tblScores b ON a.ID = b.ID AND b.Year = @Year 
    LEFT JOIN tblScores c ON a.ID = c.ID AND c.Year = @Year 
    LEFT JOIN tblScores d ON a.ID = d.ID AND d.Year = @Year 
    LEFT JOIN tblScores e ON a.ID = e.ID AND e.Year = @Year 
    LEFT JOIN tblScores f ON a.ID = f.ID AND f.Year = @Year 
WHERE c.TestC = 'Test C' 
     d.TestD = 'Test D' 
     e.TestE = 'Test E' 
     f.TestF = 'Test F' 

现在的问题是，当我增加更多的where子句和几乎相同的“测试” where子句，它给了我NULL值COUNT的一切和0。上面的代码正常工作，但我使用的测试名称非常相似，表格做得很差，因此所有“测试”名称都在一列中。我无法调试，因为现在我被困在MSSQL 05中。请帮忙！

编辑：使用下面的聚合函数SUM从EricZ越来越之后，如果任何人有兴趣我发现

AVG(CASE WHEN b.Test = 'Test D' THEN CAST(b.Score AS DEC(10,2)) ELSE NULL END) AS avgTestC 

是对AVG聚合函数的正确形式。

Answer 1

您可以使用CASE做COUNT，并且只需要连接表一旦

SELECT 
     AVG(CAST((CASE WHEN b.TestC = 'Test C' THEN b.Score ELSE 0 END) AS DEC(10,2))) AS avgTestC, 
     AVG(CAST((CASE WHEN b.TestD = 'Test D' THEN b.Score ELSE 0 END) AS DEC(10,2))) AS avgTestD, 
     AVG(CAST((CASE WHEN b.TestE = 'Test E' THEN b.Score ELSE 0 END) AS DEC(10,2))) AS avgTestE, 
     AVG(CAST((CASE WHEN b.TestF = 'Test F' THEN b.Score ELSE 0 END) AS DEC(10,2))) AS avgTestF,    
     SUM(CASE WHEN b.TestC = 'Test C' THEN 1 ELSE 0 END) AS CountC, 
     SUM(CASE WHEN b.TestD = 'Test D' THEN 1 ELSE 0 END) AS CountD, 
     SUM(CASE WHEN b.TestE = 'Test E' THEN 1 ELSE 0 END) AS CountE, 
     SUM(CASE WHEN b.TestF = 'Test F' THEN 1 ELSE 0 END) AS CountF 
FROM tblWithIds a, 
JOIN tblScores b ON a.ID = b.ID AND b.Year = @Year 

Answer 2

用例，而不是

SELECT SUM(CASE WHEN Something > 0 THEN Something ELSE 0 END) AS A, SUM(CASE WHEN Something2 > 0 THEN Something2 ELSE 0 END) AS B