拼接带分隔符字符串的细节

我最近见到有同事这样拼接字符串（SQL Server 2008 R2，CTE部分是伪造的示例数据）

 1 WITH TEMP AS
 2 (
 3 SELECT 'A' AS ITEM
 4 UNION ALL
 5 SELECT 'B' AS ITEM
 6 UNION ALL
 7 SELECT 'C' AS ITEM
 8 )
 9 SELECT A.ITEM+',' AS [data()]
10 FROM TEMP A
11 FOR XML PATH('')

这个QUERY会得到这样的XML

A, B, C,

但是潜在的问题是当数据不是字符型的时候会出问题，试把CTE中的数据全部改为数字

WITH TEMP AS
(
SELECT 1 AS ITEM
UNION ALL
SELECT 2 AS ITEM
UNION ALL
SELECT 3 AS ITEM
)
SELECT A.ITEM+',' AS [data()]
FROM TEMP A
FOR XML PATH('')

这个QUERY会报错：

Msg 245, Level 16, State 1, Line 2 Conversion failed when converting the varchar value ',' to data type int.

所以，我推荐的拼接方式是

WITH TEMP AS
(
SELECT 1 AS ITEM
UNION ALL
SELECT 2 AS ITEM
UNION ALL
SELECT 3 AS ITEM
)
SELECT A.ITEM AS [data()],','
FROM TEMP A
FOR XML PATH('')

运行结果是：

1,2,3,

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