postgresql : cross-database references are not implemented:

问题

I am trying to convert SQL inner join query into PostgreSQL inner join query. In this inner join query which tables are using that all tables are not present in one database. we separated tables into two databases i.e. application db and security db

users and permission table are present in security db
userrolemapping and department are present in application db

I tried like below but I am getting following error

Error

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

SQL Stored Function

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 Stored Function

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;

回答1:

You cannot join tables from different databases.

Databases are logically separated in PostgreSQL by design.

If you want to join the tables, you should put them into different schemas in one database rather than into different databases.

Note that what is called “database” in MySQL is called a “schema” in standard SQL.

If you really need to join tables from different databases, you need to use a foreign data wrapper.

来源：https://stackoverflow.com/questions/51784903/postgresql-cross-database-references-are-not-implemented

标签

postgresql

inner-join