我正在尝试将SQL内部连接查询转换为PostgreSQL内部连接查询。在此内部连接查询中，哪些表正在使用，所有表不存在于一个数据库中。我们将表分为两个数据库，即应用程序数据库和安全数据库
1.安全数据库中存在用户和权限表
1.应用程序数据库中存在用户角色Map和部门
我尝试了如下操作，但出现以下错误

• • 错误**

ERROR:  cross-database references are not implemented: "Rockefeller_ApplicationDb.public.userrolemapping"
LINE 4:         INNER JOIN "Rockefeller_ApplicationDb".public.userro..

• • SQL存储函数**

SELECT   Department.nDeptID 
    FROM Users INNER JOIN Permission 
         ON Users.nUserID = Permission.nUserID INNER JOIN UserRoleMapping
         ON Users.nUserID = UserRoleMapping.nUserID INNER JOIN Department
         ON Permission.nDeptInst = Department.nInstID
         AND  Department.nInstID = 60
    WHERE     
         Users.nUserID = 3;

• • PostgreSQL存储函数**

SELECT dep.ndept_id 
        FROM "Rockefeller_SecurityDb".public.users as  u 
        INNER JOIN  "Rockefeller_SecurityDb".public.permissions p ON u.nuser_id = p.nuser_id
        INNER JOIN "Rockefeller_ApplicationDb".public.userrolemapping as urm ON u.nuser_id = urm.nuser_id
        INNER JOIN "Rockefeller_ApplicationDb".public.department dep ON p.ndept_inst = dep.ninst_id
           AND  dep.ninst_id = 60
                        WHERE     
                            u.nuser_id = 3;