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SQL FULL OUTER JOIN

SQL Full Outer Join

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What is Full Outer Join in SQL?

In SQL the FULL OUTER JOIN combines the results of both left and right outer joins and returns all (matched or unmatched) rows from the tables on both sides of the join clause.

Syntax

SELECT * 
FROM table1 
FULL OUTER JOIN table2 
ON table1.column_name=table2.column_name;

Parameters

Name Description
table1, table2 Name of the tables participating in joining.
column_name Column of the participating tables.

Example :

Let’s combine the same two tables using a full join.

Sql full outer sample table image1

Code

SELECT * FROM table_A 
FULL OUTER JOIN table_B 
ON table_A.A=table_B.A;

Output:

Sql full outer output image1

Because this is a full join, all rows (both matching and nonmatching) from both tables are included in the output. There is only one match between table table_A and table table_B, so only one row of output displays values in all columns. All remaining rows of output contain only values from table table_A or table table_B, with the remaining columns set to missing values

only one row of output displays values in all columns explain below -

Sql full outer output image2

Pictorial representation

Sql full outer join image

Example :

Here is an example of full outer join in SQL between two tables.

Sample table : foods

Sample table : company

As we know the FULL OUTER JOIN is the combination of the results of both LEFT OUTER JOIN and RIGHT OUTER JOIN, so, here we are going to describe how FULL OUTER JOIN perform internally.

Pictorial Representation

Sql full outer join with left and right outer join

Here is the SQL statement which returns all rows from the 'foods' table and 'company' table using "FULL OUTER JOIN" clause.

Code

SELECT a.company_id AS "a.ComID",
a.company_name AS "C_Name",
b.company_id AS "b.ComID", 
b.item_name AS "I_Name" 
FROM   company a 
FULL OUTER JOIN foods b 
ON a.company_id = b.company_id;

Output

Sql full outer join

FULL OUTER JOIN using WHERE clause

We can include a WHERE clause with a FULL OUTER JOIN to get return only those rows where no matching data between the joining tables are exists.

The following query returns only those company that have no matching food product in foods , as well as those food product in foods that are not matched to the listed company.

Code

SELECT a.company_id AS "a.ComID", 
a.company_name AS "C_Name",
b.company_id AS "b.ComID", 
b.item_name AS "I_Name" 
FROM   company a
FULL OUTER JOIN foods b
ON a.company_id = b.company_id
WHERE a.company_id IS NULL 
OR b.company_id IS NULL 
ORDER BY company_name;

Output:

Sql full outer join with where clause image

FULL OUTER JOIN using UNION clause

A UNIOIN clause can be used as an alternate to get the same result as FULL OUTER JOIN

Here is the example:

Sql full outer sample tables

Code : using FULL OUTER JOIN

SELECT table_a.A,table_a.M,table_b.A,table_b.N 
FROM table_A 
FULL OUTER JOIN table_B 
ON table_A.a=table_b.A 
ORDER BY table_A.A;

FULL OUTER JOIN using LEFT and RIGHT OUTER JOIN and UNION clause

The following code is, the combination of LEFT OUTER JOIN and RIGHT OUTER JOIN and combined by, using UNION clause

SELECT table_a.A,table_a.M,table_b.A,table_b.N 
FROM table_A 
LEFT OUTER JOIN table_B 
ON table_A.a=table_b.A 
UNION 
SELECT table_a.A,table_a.M,table_b.A,table_b.N 
FROM table_A 
RIGHT OUTER JOIN table_B 
ON table_A.a=table_b.A;

Sql full outer join union output

Note: Outputs of the said SQL statement shown here is taken by using Oracle Database 10g Express Edition.

Key points to remember

Click on the following to get the slides presentation of all JOINS -

SQL JOINS, slide presentation

Here is a new document which is a collection of questions with short and simple answers, useful for learning SQL as well as for interviews.



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