Question

我想在select语句中使用子查询。类似的东西：

SELECT 
   (SELECT COUNT(*) FROM table2 WHERE a = '1') AS countsubquery, fielda,fieldb
FROM testtable
WHERE a = 'b'

但是当子查询为空时，整行将从结果中删除。因此，当subquery = null并填充fielda en字段b时，此行将从结果中删除，因为countsubquery = null。

结果是否有办法：

countsubquery = null
fielda = filled
fieldb = filled

在我的情况下，子查询需要在select语句中。

谢谢！

**编辑** 真实查询：

SELECT (driver.[Initials]+' '+driver.[Driver Name]) AS bedrijdernaam,
        driver.[Function] AS functie,
        leasecardriver.[Driver Code] AS personeelsnummer,
        leasecar.[Car Brand Code] AS automerk,
        leasecar.[Car Type Code] AS autotype,
        leasecar.[License No_] AS kenteken,
        (SELECT SUM(fuel.Amount) FROM [EXAMPLEDATA$Fuel Table] AS fuel 
            WHERE fuel.[Perpetration Date] >= '--01 00:00:00' 
            AND fuel.[Perpetration Date] <= '--29 11:59:00' 
            AND fuel.personnelnumber = leasecardriver.[Driver Code]) AS verbruik,
            leasecardriver.[Driver Code] AS personeelsnummer1,
            CONVERT(VARCHAR(19),leasecontract.[Expected Contract ending date],105) AS einddatum 
            FROM [EXAMPLEDATA$Lease Contract] AS leasecontract 
LEFT JOIN [EXAMPLEDATA$Lease Car] AS leasecar ON leasecontract.[License No_] = leasecar.[License No_] 
LEFT JOIN [EXAMPLEDATA$Lease Company] AS leasecompany ON leasecompany.Code = leasecontract.[Lease Company Code] 
LEFT JOIN [EXAMPLEDATA$Lease Car Driver] AS leasecardriver ON leasecardriver.license = leasecar.[License No_] 
LEFT JOIN [EXAMPLEDATA$Driver] AS driver ON leasecardriver.[Driver Code] = driver.[Driver] 
WHERE (leasecontract.[Status] = '0' OR leasecontract.[Status] = '1') 
AND (((driver.[Voornaam]+' '+driver.[Driver Name]) LIKE '%%') OR (leasecar.[License No_] LIKE '%%') OR (driver.[Cost place code] LIKE '%%') OR (driver.[BusinessLine (GP)] LIKE '%%') OR (driver.[Salaris Unit (GP)] LIKE '%%') OR (leasecardriver.[Driver Code] LIKE '%%'))

以下是“租车。[许可证号_] AS肯特肯”，

Answer 1

如果我有代表，请将此添加为评论。

如果我理解正确，语法会继续，但是你遇到了子查询结果为null的记录问题。在这种情况下，我认为值得一看： http://msdn.microsoft.com/en-us/library/ms184325.aspx

如果结果为NULL，您可以指定备用值，因此这也应显示在结果集中。

Answer 2

试试这个：

SELECT 
   COALESCE((SELECT COUNT(*) FROM table2 WHERE a = '1'),0) AS countsubquery,
   fielda,fieldb
FROM testtable
WHERE a = 'b'

SQL select子查询没有结果

2 个答案: