SQL INNER JOIN

The SQL Inner Join is one of the Join Type which returns the records (or rows) present in both tables If there is at least one match between columns. Or we can Simply say, Inner Join returns the records (or rows) present in both tables as long as the Condition after the ON Keyword is TRUE.

SQL Inner Join Syntax

The basic syntax of the Inner Join in SQL Server is as shown below:

-- SQL Server INNER JOIN Syntax
SELECT Table1.Column(s), Table2.Column(s),
FROM Table1
 INNER JOIN
     Table2 ON
   Table1.Common_Column = Table2.Common_Column

--OR We can Simply Write it as
SELECT Table1. Column(s), Table2. Column(s),f
FROM Table1
 JOIN
     Table2 ON
   Table1.Common_Column = Table2.Common_Column

In SQL Inner join is the default join so it is optional to use the INNER Keyword. Let us see the visual representation of the Inner join for better understanding.

From the above image, you can understand easily that, Inner join only displays the matching records from Table 1 and Table 2 (Like an Intersect in Math)

In this article, we will show you, How to write Inner Join in SQL Server. For this, We are going to use two tables (Employee and Department) present in our [SQL Server Tutorials] Database.

Data present in the Employee Table is:

Data present in the Department Table is:

SQL Inner Join – Selecting All Columns

The following SQL Query will display all the columns present in Employees and Department tables

-- SQL Server INNER JOIN Example
SELECT *
FROM [Employee]
   INNER JOIN
     [Department] ON
 [Employee].[DepartID] = [Department].[id]

OUTPUT

Let me avoid the INNER Keyword

-- SQL Server INNER JOIN Example
SELECT *
FROM [Employee]
   JOIN
     [Department] ON
 [Employee].[DepartID] = [Department].[id]

OUTPUT

If you observe the above screenshot, Although we had 15 records in the Employee table, an Inner join is displaying 11 records. This is because, Department Id for the remaining 4 records (i., ID number 10, 11, 14 and 15) in Employee table are NULLS.

NOTE: The [Department ID] column is repeated twice, which is annoying to the user. By selecting individual column names we can avoid unwanted columns so, Please avoid SELECT * Statements in INNER JOINS

SQL Inner Join – Selecting Few Columns

Please place the required columns after the SELECT Statement to avoid unwanted columns

-- SQL Server INNER JOIN Example
SELECT [FirstName]
      ,[LastName]
      ,[DepartmentName]
FROM [Employee]
  INNER JOIN
     [Department] ON
  [Employee].[DepartID] = [Department].[id]

OUTPUT

Above query will perfectly work as long as the column names from both tables (Employee and Department) are different like above. What happens if we have the same Column names in both the tables? Well, you will end up in a mess. Let us see how to resolve the issue.

Before we get into the solution, let me show you one practical example. As you can see, we are using the above query but we added id from department table as an additional column.

-- SQL Server INNER JOIN Example
SELECT [FirstName]
      ,[LastName]
      ,id
      ,[DepartmentName]
FROM [Employee]
INNER JOIN
     [Department] ON
           [Employee].[DepartID] = [Department].[id]

You can see from the below screenshot, it is throwing an error: Ambiguous column name id. This is because, id column is present in both Employee, and department table. And SQL Server doesn’t know which column you are asking it to retrieve.

To resolve these kinds of issues you always have to use table name before the column name. The following query is using ALIAS table name before the column names. By this approach, we can inform the SQL Server, that we are looking for id column belonging to the department table.

We can simply write the above query as:

-- SQL Server INNER JOIN Example
SELECT Emp.[FirstName] AS [First Name]
      ,Emp.[LastName] AS [Last Name]
	  ,Dept.id 
      ,Dept.[DepartmentName] AS [Department Name]
FROM [Employee] AS Emp
INNER JOIN
     [Department] AS Dept ON
    Emp.[DepartID] = Dept.[id]

OUTPUT

Use Where Clause in SQL Inner Join

The SQL Server also allows us to use Where Clause to restrict the number of rows returned by the Inner Join. In this example, we will use that WHERE Clause along with the Inner Join.

-- SQL Server Inner Join Example
SELECT Emp.[FirstName] AS [First Name]
      ,Emp.[LastName] AS [Last Name]
      ,Dept.[DepartmentName] AS [Department Name]
FROM [Employee] AS Emp
INNER JOIN
     [Department] AS Dept ON
			Emp.[DepartID] = Dept.[id]
WHERE Dept.[DepartmentName] = 'Software Developer' OR
		Dept.[DepartmentName] = 'Sr. Software Developer'

OUTPUT

SQL Inner Join – Order By Clause

The SQL Server allows us to use Order By Clause to rearrange the order of the records.

-- SQL Server INNER JOIN Example
SELECT Emp.[FirstName] AS [First Name]
      ,Emp.[LastName] AS [Last Name]
      ,Dept.[DepartmentName] AS [Department Name]
FROM [Employee] AS Emp
INNER JOIN
     [Department] AS Dept ON
    Emp.[DepartID] = Dept.[id]
ORDER BY [FirstName] ASC

OUTPUT

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