Postgresql error cross database references are not implemented

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

1. users and permission table are present in security db
2. 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;

For future searchs, you can to use dblink to connect to other database.

Follow commands:

create extension dblink;

SELECT dblink_connect('otherdb','host=localhost port=5432 dbname=otherdb user=postgres password=???? options=-csearch_path=');

SELECT * FROM dblink('otherdb', 'select field1, field2 from public.tablex')
AS t(field1 text, field2 text);

answered Jul 22, 2020 at 11:58

New to postrgreSQL and I had the same requirement. FOREIGN DATA WRAPPER did the job.

IMPORT FOREIGN SCHEMA — import table definitions from a foreign server

But first I had to:

1. enable the fdw extension

2. define the foreign server (which was the locahost in this case!)

3. create a mapping between the local user and the foreign user.

CREATE EXTENSION postgres_fdw;

CREATE SERVER localsrv
FOREIGN DATA WRAPPER postgres_fdw
OPTIONS (host 'localhost', dbname 'otherdb', port '5432');

CREATE USER MAPPING FOR <local_user>
SERVER localsrv
OPTIONS (user 'ohterdb_user', password 'ohterdb_user_password');

IMPORT FOREIGN SCHEMA public
FROM SERVER localsrv 
INTO public;

After that I could use the foreign tables as if they were local. I did not notice any performance cost.

In my case, I changed my query from:

SELECT * FROM myDB.public.person

to this:

SELECT * FROM "myDB".public.cats

and it worked.

You can read more at mathworks.com.

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

1. users and permission table are present in security db
2. 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;

For future searchs, you can to use dblink to connect to other database.

Follow commands:

create extension dblink;

SELECT dblink_connect('otherdb','host=localhost port=5432 dbname=otherdb user=postgres password=???? options=-csearch_path=');

SELECT * FROM dblink('otherdb', 'select field1, field2 from public.tablex')
AS t(field1 text, field2 text);

answered Jul 22, 2020 at 11:58

New to postrgreSQL and I had the same requirement. FOREIGN DATA WRAPPER did the job.

IMPORT FOREIGN SCHEMA — import table definitions from a foreign server

But first I had to:

1. enable the fdw extension

2. define the foreign server (which was the locahost in this case!)

3. create a mapping between the local user and the foreign user.

CREATE EXTENSION postgres_fdw;

CREATE SERVER localsrv
FOREIGN DATA WRAPPER postgres_fdw
OPTIONS (host 'localhost', dbname 'otherdb', port '5432');

CREATE USER MAPPING FOR <local_user>
SERVER localsrv
OPTIONS (user 'ohterdb_user', password 'ohterdb_user_password');

IMPORT FOREIGN SCHEMA public
FROM SERVER localsrv 
INTO public;

After that I could use the foreign tables as if they were local. I did not notice any performance cost.

In my case, I changed my query from:

SELECT * FROM myDB.public.person

to this:

SELECT * FROM "myDB".public.cats

and it worked.

You can read more at mathworks.com.