sql-server - TSQL 如何按文字分组？

Question

我将这个问题简化为一个非常简单的形式:

SELECT
'A' AS [Literal]
UNION 
SELECT
'B' AS [Literal]
GROUP BY
[Literal]

我收到消息:

Msg 207, Level 16, State 1, Line 7 Invalid column name 'Literal'.

我试过了，结果是一样的:

SELECT
t.literal FROM 
(SELECT 'A' AS [Literal]) t
UNION 
SELECT
'B' 
GROUP BY
[Literal]

Answer 1

当您想要 GROUP BY 时，您需要一个派生表一个UNION :

SELECT X.[Literal], [Count] = COUNT(*)
FROM(
    SELECT [Literal] = 'A'
    UNION ALL 
    SELECT [Literal] = 'B'
) X
GROUP BY X.[Literal]

Demo