使用CTE简化SQL语句

Question

我有如下查询:

SELECT A.a, A.b, B.c,
(CASE WHEN ... THEN ... ELSE ... END) AS CalculatedValue,
B.d
FROM    dbo.TableA A INNER JOIN
        dbo.TableB B ON (...)
WHERE (CASE WHEN ... THEN ... ELSE ... END) BETWEEN @DayStart AND @DayEnd
GROUP BY A.a, (CASE WHEN ... THEN ... ELSE ... END), B.c

避免重复多次完全相同的表达式:(CASE WHEN ... THEN ... ELSE ... END)我想在select中定义一个CTE并查询这样的表,where和group by表达式CalculatedValue

不幸的是,这不起作用,因为选择需要已经包括group by创建时CTE

有没有其他方法可以用来不重复CASE WHEN...这么多次？

Answer 1

使用CROSS APPLY,可用于定义别名字段,然后引用它们:

SELECT A.a, 
       A.b, 
       B.c,
       CalculatedValue,
       B.d
FROM    
       dbo.TableA A 
INNER JOIN
        dbo.TableB B 
        ON (...)
CROSS APPLY 
        (SELECT (CASE WHEN ... THEN ... ELSE ... END)) CxA(CalculatedValue)
WHERE CalculatedValue BETWEEN @DayStart AND @DayEnd
GROUP BY A.a, CalculatedValue, B.c

这CxA只是一个别名,您可以随意命名.