string_agg（字符变化）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')

我正在尝试将上述 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')

执行我的 postgresql 查询时遇到以下错误

string_agg（字符变化，字符变化，字符变化，字符变化）不存在。没有提示匹配给定的名称和参数类型。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。直接聚合即可：

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'

---

错误消息源于您尝试使用四个 (varchar) 参数调用 string_agg() 函数。但是string_agg() 是defined 只接收两个参数（要聚合的值和分隔符）。