string_agg(character_varying)不存在

Question

我正在从MSSQL迁移到PostgreSQL。

MSSQL查询：

SELECT * FROM dbo.Mtr_userdetails AS table1 JOIN( SELECT urmo.urm_userid STUFF((SELECT ',' + urm.urm_role_name FROM dbo.STL_CS_Mtr_userrolemapping urm WHERE urm.urm_userid = 'test2' AND urm.urm_status = 'A' AND urm.urm_appid = 'BCA' FOR XML PATH('')),1,1,'') [user_roles],urmo.urm_appid FROM dbo.Mtr_userrolemapping urmo WHERE urmo.urm_appid = 'BCA' AND urmo.urm_userid = 'test2' GROUP BY urmo.urm_userid,urmo.urm_appid) AS table2 ON table1.ud_userid = table2.urm_userid WHERE (table1.ud_userid = 'test2')

我正在尝试将上面的ms sql查询转换为postgresql语法。

PostgreSQL查询：

SELECT *
FROM STL_Mtr_userdetails AS table1
  JOIN (
    SELECT urmo.urm_userid,
           string_agg((SELECT ',' || urm.urm_role_name 
                       FROM STL_CS_Mtr_userrolemapping urm
                       WHERE urm.urm_userid = 'test2' 
                         AND urm.urm_status = 'A' 
                         AND urm.urm_appid = 'BCA')::varchar, 1::varchar, 1::varchar, ''::varchar) user_roles,
           urmo.urm_appid
    FROM STL_CS_Mtr_userrolemapping urmo
    WHERE urmo.urm_appid = 'BCA'
      AND urmo.urm_userid = 'test2'
    GROUP BY urmo.urm_userid,
             urmo.urm_appid
  ) AS table2 ON table1.ud_userid = table2.urm_userid
WHERE (table1.ud_userid = 'test2')

执行postgresql查询时，我将面临以下错误

String_agg(字符变化，字符变化)不存在。没有任何提示与给定的名称和参数类型匹配。您可能需要添加显式类型转换。

Answer 1

不需要复杂的嵌套标量子选择。只需直接汇总：

SELECT *
FROM STL_Mtr_userdetails AS table1
  JOIN (
    SELECT urmo.urm_userid,
           string_agg(urm.urm_role_name, ',') as user_roles
    FROM STL_CS_Mtr_userrolemapping urmo
    WHERE urmo.urm_appid = 'BCA'
    GROUP BY urmo.urm_userid
  ) AS table2 ON table1.ud_userid = table2.urm_userid
WHERE table1.ud_userid = 'test2'

错误消息产生于这样一个事实，即您试图用4个(varchar)参数调用一个string_agg()函数。但是string_agg()是已定义，只接收两个参数(要聚合的值和分隔符)。