what is self join

1SELECT
2    e.first_name + ' ' + e.last_name employee,
3    m.first_name + ' ' + m.last_name manager
4FROM
5    sales.staffs e
6INNER JOIN sales.staffs m ON m.staff_id = e.manager_id
7ORDER BY
8    manager;

1SELECT column_name(s)
2FROM table1 T1, table1 T2
3WHERE condition;

1Self is joining a table to itself.
2
3-- assume employee table as 2 different table using different alias 
4-- as  manager and worker 
5-- we want to join these 2 virtual manager and worker table 
6-- to get manager's first name and worker's first name 
7-- our condition is worker's manager_id match managers employee id
8
9SELECT  manager.FIRST_NAME AS MANAGER_NAME , 
10        worker.FIRST_NAME AS WORKER_NAME 
11FROM EMPLOYEES manager 
12INNER JOIN EMPLOYEES worker on worker.MANAGER_ID = manager.EMPLOYEE_ID  
13
14order by 1 
15;