Question

I need to write a self join query

My Table is:-

id locid parentid filename 

1    1      0       word 
2    1      0       excel 
3    1      1       power 
4    2      0       word 
5    2      4       power 

I need to retrive only those data where parentid=0 using selfjoin

Thanks in Advance

Answer 1

From your query its not clear based on which do u want to use self join.

Anyway below is one example which will give u clear picture about self join.

Suppose Employees is table which contains data related to employees.
An Employee can be manager for other employee but single itself consider as employee for any organization.

Exmaple:

TableName : employees

EmployeeID  EmployeeName    ManagerID         
    1            A            null         
    2            B             1         
    3            C             1         
    4            D             3         
    5            E             3 

Query:

select e1.EmployeeName as Employee,
    e2.EmployeeName as ReportsTo
from employees e1 
left outer join employees e2
on e1.ManagerID  = e2.EmployeeID 
order by e1.EmployeeID 

OutPut will be as below:

Employee  Reports To
-------- ----------- 
  B          A    
  C          A    
  D          C    
  E          C