SQL SELF JOIN

The SQL Self Join is one of the Join Type that is used to Join Table 1 to Itself. If we have the Primary key and Foreign key in the same table then, we can use this Self join to connect them.

In this article we will show you, How to write Self Join in SQL Server. The basic syntax of the Self Join in SQL Server is as shown below:

-- Syntax for SQL Server Self Join
SELECT Tab1.Column(s), Tab2.Column(s),
FROM Table1 AS Tab1, 
     Table1 AS Tab2

NOTE: ALIAS Table Name is mandatory for Self Join

For this demo, We are going to use Employees table present in our SQL Server Database. Data present in the Employees Table is:

From the above screenshot, you can observe that we have 15 different employees and each person belongs to the Department and we have the Foreign key column DepartID.

SQL Self Join Example

In general, Every Department will have one Department Head and he will definitely belong to one of the Employee. To get the Department Head name we have to use the Self Join using the Primary key & Foreign key.

For example, The following Self Join Query will display the Name of the Department Head for each and every Employee present in the Employees table.

-- SQL Server Self Join Example
SELECT EMP1.[FirstName]
      ,EMP1.[LastName]
   ,EMP1.[Department Name]
   ,EMP2.[FirstName] +' '+ EMP2.[LastName] AS [Department Head]
  FROM [Employees] AS EMP1, [Employees] AS EMP2
  WHERE EMP1.DepartID = EMP2.ID

OUTPUT

If you observe the above screenshot, Rob Walter is not only Sr. Software Developer but also Department Head for the remaining Sr. Software Developer in an organization.