The SQL Full Join or Full Outer Join is a SQL Join Type used to return all the records (or rows) present in both the Left table and the right table. All the Unmatched rows filled with NULL Values.
The SQL Server Full Outer join can also call 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 the Sql Server Full Outer join displays all the records present in Table 1 and Table 2
SQL Full Join Syntax
The 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
For this SQL Server Full Join demonstration, 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 SQL Server Department Table is:
Full Join Select All Columns
The following Sql Server Full Outer Join Select all columns 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, SQL Full Outer Join is displaying 17 records. It 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 and 4 (Module Lead and Team Lead), there are no matching records in the Employees table, so NULLS replaces them.
- ID number 10, 11, 14 and 15 of [DepartID], id, [Department Name], it is displaying NULL Values. It is because the Department Id for them in the Employee table is NULLS, so there are no matching records in the right table.
Full Join without Outer keyword
As we said before, it is optional to use an Outer keyword in this Join type. 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
Full Join Select Few Columns
Please place the required columns after the SELECT Statement to avoid unwanted columns in full outer join
-- SQL Server FULL JOIN Example SELECT [FirstName] ,[LastName] ,[DepartmentName] FROM [Employee] FULL JOIN [Department] ON [Employee].[DepartID] = [Department].[id]
OUTPUT
Above SQL Full Join 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. Still, we added id from the 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]
As you can see from the below screenshot, it is throwing an error: Ambiguous column name id. It is because the 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 issue, you always have to use the table name before the column name.
The following Full outer Join query is using the 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 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
SQL Full Join Where Clause
The Full Outer Join 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 Full outer Join 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