我有两个表User和User_Roles。用户可以拥有多个角色。
用户表
User_Id User_Name
1 Edward
2 John
3 Mark
USER_ROLES TABLE
User_ID Role
1 Admin
1 Writer
1 Form
2 Writer
3 Form
3 Writer
我想写一个查询,给我以下结果
User_ID User_Name Role
1 Edward Admin, Writer,Form
2 John Writer
3 Mark Form,Writer
我尝试过使用GROUP BY
,我知道这是我可以得到的结果,但我只是做得不对。
SELECT COUNT(T0.[User_Id]),T0.[User_Name],T1.[Role]
FROM USER T0
INNER JOIN USER_ROLES T1 ON T0.User_ID = T1.User_ID
GROUP BY T0.[User_Name], T1.[Role]
我使用COUNT
仅用于测试目的,因为当我使用聚合函数执行GROUP BY
时,我收到错误。
使用聚合和STRING_AGG()
(可从SQL Server 2017开始):
SELECT u.User_ID, u.User_Name, STRING_AGG(r.Role, ',') AS Roles
FROM user u
INNER JOIN user_roles r ON r.User_Id = u.User_Id
GROUP BY u.User_ID, u.User_Name
注意:您可能希望对聚合字符串进行排序,以便获得可预测的值,例如:
STRING_AGG(r.Role, ',') WITHIN GROUP (ORDER BY r.Role) AS Roles
另一种选择是FOR XML XML / STUFF技巧:
SELECT
U.USER_NAME,
STUFF((SELECT ',' + UR.ROLE
FROM [USER_ROLES] UR
WHERE UR.USER_ID = U.USER_ID
FOR XML PATH('')), 1, 1, '') [ROLES]
FROM [USER] U
GROUP BY U.USER_NAME, U.USER_ID
ORDER BY 1