如何编写sql从多个行转换一个字符串？

Question

Supose I have a table with following kind of data:

Tab(id, myString)
1  A
2  B
3  C
...

I want to a SQL can return all one string for all values in Column myString. So the result I want looks like: "A, B, C"

If I don't want to use cursor and stored procedure, is it possible sql to get such kind of result?

Answer 1

Use T-SQL row concatenation:

declare @s varchar(max)
set @s = ''
select @s = @s +
 case when @s = '' then '' else ', ' end + Letter
from MyTable

select @s

edited removed trailing ", "

Answer 2

A combination of using FOR XML PATH (providing an empty element name) and STUFF is a common SQL Server (2005+) technique. It doesn't require declaration of any local variables and can therefore be run outside of batch or procedure.

SELECT STUFF(
(SELECT ',' + t.myString
FROM TAB t
ORDER BY t.Id
FOR XML PATH('')),1,1,'') AS CSV

Answer 3

Declare @tbl table(ID nvarchar(1),[myString] nvarchar(100))
Insert into @tbl values(1,'A'); 
Insert into @tbl values(2,'B'); 
Insert into @tbl values(3,'C'); 
DECLARE @CSVList varchar(100)

SELECT @CSVList = COALESCE(@CSVList + ' , ', '') + 
   [myString]
FROM @tbl


SELECT @CSVList