SQL Query Performance Query

Question

I have a hierarchy like following Group Company Department Cost Centre Which are being stored in database like following table structure.

Table Name : OrgHierarchy Columns : Id, ParentId, Level, Type

In My Employee View I have employee Cost Centre, Department, Company and Group present.

I need help in writing better performing query to find employee for a particular node in the hierarchy (it can be Group/Company/Department/Cost Centre)

  Select * from vw_Employee  emp
    Where emp.CostCentreId = @NodeId 
    OR emp.DepartmentId=@NodeId 
    OR emp.CompanyId=@NodeId 
    OR emp.GroupId= @NodeId

Here the number of “OR” statement making the query very slow.

Is there any better approach to handle the efficiently or any other approach?

Answer 1

Using OR in condition makes indexis be skipped. Replace it with UNION :

Select * 
from vw_Employee  emp
Where emp.CostCentreId = @NodeId 
UNION
Select * 
from vw_Employee  emp
Where emp.DepartmentId=@NodeId 
UNION
Select * 
from vw_Employee  emp
Where emp.CompanyId=@NodeId 
UNION
Select * 
from vw_Employee  emp
Where emp.GroupId= @NodeId

Here is a good question.