Question

我需要一个嵌套查询，但是有条件地定义了内部选择sql。

这不起作用：

SELECT inner.a, inner.b, t4.c FROM 
CASE
  WHEN (@Param1 = 1) THEN
    ( SELECT t1.col1 AS a , t2.col2 AS b
      FROM Table1 t1 
      INNER JOIN Table2 t2 ON t2.pk = t1.fk2 ) AS inner
  WHEN (@Param2 = 2) THEN
   ( SELECT t1.col1 AS a , t3.col3 as b
     FROM Table1 t1 
     LEFT JOIN Table3 t3 ON t3.pk = t1.fk3 ) AS inner
END
LEFT JOIN Table4 t4 ON t4.pk = inner.b
WHERE inner.a = @Param1

Answer 1

SELECT inner1.a, inner1.b, outer1.c 
FROM ( SELECT t1.col1 AS a , t2.col2 AS b
      FROM Table1 t1 
      INNER JOIN Table2 t2 ON t2.pk = t1.fk2 ) AS inner1
    LEFT JOIN Table4 t4 ON t4.pk = inner1.b
WHERE @Param1=1
    AND inner1.a = @Param1


UNION ALL 

SELECT inner1.a, inner1.b, outer1.c 
FROM ( SELECT t1.col1 AS a , t3.col3 as b
     FROM Table1 t1 
     LEFT JOIN Table3 t3 ON t3.pk = t1.fk3 ) AS inner1
LEFT JOIN Table4 t4 ON t4.pk = inner1.b
WHERE @Param2 =2 
    inner1.a = @Param1

Answer 2

试试这个：

SELECT  InnerTable.a, InnerTable.b, t4.c
FROM    (   SELECT  t1.col1 AS a, t2.col2 AS b
            FROM    Table1 t1 INNER JOIN
                    Table2 t2 ON t2.pk = t1.fk2
            WHERE   @Param1 = 1

            UNION

            SELECT  t1.col1 AS a, t3.col3 AS b
            FROM    Table1 t1 LEFT JOIN
                    Table3 t3 ON t3.pk = t1.fk3
            WHERE   @Param2 = 2
        ) AS InnerTable
        LEFT JOIN Table4 t4 ON t4.pk = InnerTable.b
WHERE   InnerTable.a = @Param1

Answer 3

你不能这样使用，为此使用dynamic query并执行字符串

如果需要，也可以动态添加where条件。

像

 DECLARE @SelectStatement NVARCHAR(2000)

DECLARE @FullStatement NVARCHAR(4000)

SET @SelectStatement = 'SELECT TOP 5 * FROM SalesHistory '

SET @FullStatement = @SelectStatement + ISNULL(@WhereClause,'')

PRINT @FullStatement

EXECUTE sp_executesql @FullStatement

t-sql嵌套查询，内部选择有条件地定义

3 个答案: