SQL Server分组连接并去重类似Mysql的Group_Concat功能实现

-- 建表
CREATE TABLE TestA(id int, name varchar(10));
-- 插入测试数据
INSERT INTO TestA VALUES(1, 'aa');
INSERT INTO TestA VALUES(1, 'bb');
INSERT INTO TestA VALUES(1, 'bb');
INSERT INTO TestA VALUES(1, 'eeac');
INSERT INTO TestA VALUES(2, 'cc');
INSERT INTO TestA VALUES(2, 'dd');
INSERT INTO TestA VALUES(2, 'dd');
INSERT INTO TestA VALUES(2, 'ff33');
INSERT INTO TestA VALUES(3, '111');
INSERT INTO TestA VALUES(3, '222');
--测试查询
select * from TestA
-- FOR XML PATH用法，行转列，将某一字段的所有行值连接为一个字段
SELECT '[ '+name+' ]' FROM TestA FOR XML PATH('')
--分组连接方法一：
SELECT distinct(id),name = stuff((SELECT ',' + name FROM TestA t WHERE t.id = TestA.id FOR xml path('')) , 1 , 1 , '') FROM TestA 
--分组连接方法二：
--里面一层查出单独的name，拼成一行，然后使用where条件连接外层,最终发现后面会多一个,号
SELECT id, (SELECT name+',' FROM TestA  WHERE id=a.id  FOR XML PATH('')) AS names FROM TestA a  GROUP BY id
-- 用Left去掉最后那个空格
SELECT a.id, Left(names,len(names)-1) as names from (SELECT id, (SELECT name+',' FROM TestA  WHERE id=a.id  FOR XML PATH('')) AS names FROM TestA a  GROUP BY id) a
 
--实现分组行转列连接并去重,stuff
SELECT distinct(id),name = stuff((SELECT ',' + name FROM TestA t  WHERE t.id = TestA.id GROUP BY name FOR xml path('')) , 1 , 1 , '') FROM TestA 
--实现分组行转列连接并去重,left
SELECT a.id, Left(names,len(names)-1) as names from (SELECT id,  (SELECT name+',' FROM TestA  WHERE id=a.id GROUP BY name FOR XML PATH('')) AS names FROM TestA a  GROUP BY id) a
 
--当然这个去重也可以采用distinct来实现
SELECT distinct(id),name = stuff((SELECT distinct ',' + name FROM TestA t  WHERE t.id = TestA.id FOR xml path('')) , 1 , 1 , '') FROM TestA 

效果：

正常查询：

分组连接成一个字段

分组连接并去重