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 |