Question

I am using Self Join to retrieve data from SQLSERVER Database and displaying the data in GridView.

Data in DepartmentMst table:

DepartmentID      DepartmentName       IsActive DepartmentParentID
3                    Admin Panel       1              0
4                    Human Resource    1              0
5               Information Technology 1              0
6                     Operational      1              0
21                    TestDepartment   1              3
22                       Logistics     1              3

From above data you can see that AdminPanel Department has its SubDepartment TestDepartment and Logistics with both DepartmentParentID=3 which belongs to main Department i.e AdminPanel.

Now want to display the Data in grid view which will show the DepartmentName and its SubDepartments.

My Query:

SELECT  dpt1.DepartmentID as DepartmentID
         ,dpt1.DepartmentName as DepartmentName
        ,dpt1.DepartmentParentID as ParentDepartmentID
        ,dpt2.DepartmentName as ChildDepartment
        ,dpt1.IsActive
  FROM DepartmentMst dpt1,DepartmentMst dpt2
  where (dpt1.DepartmentID=dpt2.DepartmentParentID) and dpt2.IsActive=1
  order by DepartmentID

O/P:

DepartmentID    DepartmentName  ParentDepartmentID  ChildDepartment  IsActive
3                   Admin Panel    0                   TestDepartment    1
3                   Admin Panel    0                     Logistics      1

But, I need all the DepartmentName with SubDepartmentName. If any Department has no Parent i.e DepartmentParentID=0, then it must be Shown as MainDepartment else its Parent Department Name

Eg:

DepartmentID    DepartmentName  IsActive    DepartmentParentID  ParentDeptName
3                   Admin Panel     1             0                MainDept
4                 Human Resource    1             0                MainDept
5          Information Technology   1             0                MainDept
6                     Operational   1             0                MainDept
21                 TestDepartment   1             3              AdminPanel
22                  Logistics       1             3              AdminPanel

How to get the above out put?
Help Appreciated!

Answer 1

Use a LEFT JOIN:

SELECT
    dpt1.DepartmentID as DepartmentID
    ,dpt1.DepartmentName as DepartmentName
    ,dpt2.DepartmentParentID as ParentDepartmentID
    ,ISNULL(dpt2.DepartmentName, 'MainDept') as ParentDepartment
    ,dpt1.IsActive
FROM DepartmentMst dpt1
    LEFT JOIN DepartmentMst dpt2
        ON (dpt2.DepartmentID = dpt1.DepartmentParentID) and dpt2.IsActive=1
ORDER BY DepartmentID

If the join condition has no match then all columns from dpt2 will come back as NULL so you can test for that.

Edit: I tried to fix the columns in your query as they didn’t seem correct. dpt1 is your “current” table and dpt2 is where the parent will be (if any)