PostgreSql - Relationships(joins)

How to connect Two Database in innerjoin? 1.Most Important step is Create Extension. CREATE EXTENSION dblink; Example: SELECT e . name , d . dept_name FROM Employee e JOIN dblink ( 'dbname=department_db' , 'SELECT dept_id, dept_name FROM Department' ) AS d ( dept_id INT , dept_name TEXT ) ON e . department_id = d . dept_id ; Same Database: Example: SELECT e.name, d.dept_name FROM Employee e INNER JOIN Department d ON e.dept_id = d.dept_id; Now we Start , Tables Setup Employee table: emp_id name dept_id 1 Udaya 2 2 Mathavi 3 3 Kumar 1 4 Meena NULL Department table: dept_id dept_name 1 IT 2 Finance 3 HR 4 Marketing INNER JOIN SELECT e . name , d . dept_name FROM Employee e INNER JOIN Department d ON e . dept_id = d . dept_id ; Output: name dept_name Udaya Finance Mathavi HR Kumar IT !..Only employees with valid department. LEFT JOIN SELECT e . name , d . dept_name FROM Employee e LEFT JOIN Department d ON e . dept_id = d . dept_id ; Output: name dept_name Udaya Finance Priya HR Kumar IT