The SQL Full Join (or Full Outer Join) returns 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:
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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 2014. 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
T-SQL CODE
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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 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 is no matching records in right table.
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
T-SQL CODE
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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 same Column names in both the tables? Well, you will end up in a mess. Let us see how to resolve the issue.
The following query is using table name before the column name and also used the SQL ALIAS names to rename the column names. By this approach we can inform the Database that we are looking for columns belonging to particular table.
T-SQL CODE
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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
Although we don’t have any common column names, Imagine we have [DepartmentName] column in Employee as well and we want to display Department Columns in both the tables.
We can simply write as
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SELECT Emp.[FirstName] AS [First Name] ,Emp.[LastName] AS [Last Name] ,Emp.[DepartmentName] AS [Employee Department] ,Dept.[DepartmentName] AS [Department Name] FROM [Employee] AS Emp FULL JOIN [Department] AS Dept ON Emp.[DepartID] = Dept.[id] ORDER BY [DepartmentName] ASC |
NOTE: It is always best practice to use the table name before the Column name in Joins. For example, SELECT Employee.Firstname
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