Self join is just like any other join, except that two instances of the same table will be joined in the query. Here is an example: Employees table which contains rows for normal employees as well as managers. So, to find out the managers of all the employees, you need a self join.

CREATE TABLE emp

(

empid int,

mgrid int,

empname char(10)

)

INSERT emp SELECT 1,2,'Vyas'

INSERT emp SELECT 2,3,'Mohan'

INSERT emp SELECT 3,NULL,'Shobha'

INSERT emp SELECT 4,2,'Shridhar'

INSERT emp SELECT 5,2,'Sourabh'

SELECT t1.empname [Employee], t2.empname [Manager]

FROM emp t1, emp t2

WHERE t1.mgrid = t2.empid

Here's an advanced query using a LEFT OUTER JOIN that even returns the employees without managers (super bosses)

SELECT t1.empname [Employee], COALESCE(t2.empname, 'No manager') [Manager]

FROM emp t1

LEFT OUTER JOIN

emp t2

ON

t1.mgrid = t2.empid