如何将多行作为字符串放入一行？

Question

我有两张桌子"一对多":

表格1

ID    Name
1     Abe
2     David
3     Orly

表2

ID    email
1     a@zz.com
1     ab@zz.com
1     abe@zz.com
2     dav@zz.com
2     d@zz.com
3     orly@zz.com
3     o@zz.com

我需要这样的输出:

1 Abe a@zz.com, ab@zz.com, abe@zz.com
2 David dav@zz.com, d@zz.com
3 Orly orly@zz.com, o@zz.com

我知道这不起作用,因为内部SELECT不是单个字符串:

SELECT 
    ID, Name, 
    (SELECT email FROM Table2  WHERE Table2.ID = Table1.ID) AS emails 
FROM Table1

我试着申请:

DECLARE @emails VARCHAR(999)

SELECT [ID],[Name], 
     (SELECT @emails = COALESCE(@emails + ', ', '') + [email] 
      FROM Table2) AS 'emails' 
FROM Table1

但没有运气.

该如何解决？

谢谢.

Answer 1

实现这一目标的最佳方法之一是将For XML Path和STUFF组合如下:

SELECT
    ID, Name, 
    Emails = STUFF((
        SELECT ', ' + Email FROM Table2 WHERE Table2.ID = Table1.ID
        FOR XML PATH ('')),1,2,'')
FROM Table1

Answer 2

SELECT  *
FROM    Table1 a
CROSS APPLY --or OUTER APPLY
(
    SELECT SUBSTRING(
        (SELECT ','+b.Email
        FROM    Table2 b
        WHERE   a.ID = b.ID
        FOR XML PATH(''))
        ,2
        ,4000) GroupConcat
) x

结果:

ID Name  GroupConcat
-- ----- -----------------------------
1  Abe   a@zz.com,ab@zz.com,abe@zz.com
2  David dav@zz.com,d@zz.com
3  Orly  orly@zz.com,o@zz.com