SELF JOIN the name itself tells that, in SELF JOIN it JOIN the table with itself. SELF JOIN look like it JOIN two copies of same table. Actually it won't copied, SELF JOIN works like that.

SELECT a.column1, a.column2, b.column1,b.column2,…
FROM table a, table b WHERE a.column1 = b.column2;

consider employee_details table as follows -

Scenario – Fetching details from table by using SELF JOIN.

Requirement - Fetching details from employee_details table by using SELF JOIN. The query was as follows –

SELECT a.emp_id, b.emp_name, a.salary 
FROM employee_details a, employee_details b 
WHERE a.emp_id <> b.emp_id AND a.salary < b.salary ;

By executing above query we can get output like as follows –