SQL FULL JOIN | SQL Full Outer Join

The SQL Full Join (or Full Outer Join) is a Join used to return all the records (or rows) present in both Left table and the right table. All the Unmatched rows will be filled with NULL Values.

SQL Full Join Syntax

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

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

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

TIP: In SQL Server, Full Outer join can also be called as Full Join. So it is optional to use the Outer Keyword.

Let us see the visual representation of the SQL Full join for better understanding.

From the above image, you can understand easily that, Full Outer join displays all the records present in Table 1 and Table 2

In this article, we will show you, How to write Full 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 Full Join – Selecting All Columns

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

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

OUTPUT

If you observe the above screenshot, Although We have 15 records in the Employee table, Full Join is displaying 17 records. This is because there are two records in the Department table i.e., Department Id 3, 4 (Module Lead and Team Lead) so 15 + 2 = 17 total records.
For Department Id 3, 4 (Module Lead and Team Lead) there is no matching records in Employees table so they are simply replaced by NULLS.
For [DepartID], id, [Department Name] it is displaying NULL Values for the ID number 10, 11, 14 and 15 . This is because Department Id for them in Employee table are NULLS so there are no matching records in right table.

SQL Full Join – Avoid Outer keyword

As we said before, it is optional to use an Outer keyword. Let me remove the Outer keyword, and work will FULL JOIN

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

OUTPUT

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 Full Join

SQL Full Join – Selecting Few Columns

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

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

OUTPUT

Use Where Clause in SQL Full Join

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

-- SQL Server FULL JOIN Example
SELECT Emp.[FirstName] AS [First Name]
      ,Emp.[LastName] AS [Last Name]
      ,Dept.[DepartmentName] AS [Department Name]
FROM [Employee] AS Emp
  FULL OUTER JOIN
     [Department] AS Dept ON
    Emp.[DepartID] = Dept.[id]
WHERE Dept.[DepartmentName] IS NOT NULL

OUTPUT

SQL Full Join – Order By Clause

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

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

OUTPUT

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