MySQL - Full Join

Table of content

MySQL Full Join creates a new table by joining two tables as a whole. The joined table contains all records from both the tables and fill in NULLs for missing matches on either side. In short, full join is a type of outer join that combines the results of both left and right joins.

MySQL Full Join

In MySQL, there is no provision to perform full join operation. We can, however, imitate this operation to produce the same results.

The result-set obtained from performing full join is a union of result-sets obtained from left join and right join. Thus, we can first retrieve result-sets from left and right join operations and combine them using the UNION keyword.

But, this method only works for cases where duplicate records are non-existent. If we want to include the duplicate rows, using UNION ALL keyword to combine the result-sets is preferred.

Syntax

Following is the basic syntax to emulate Full Join −

SELECT table1.column1, table2.column2...
FROM table1
LEFT JOIN table2
ON table1.common_field = table2.common_field

[UNION | UNION ALL]

SELECT table1.column1, table2.column2...
FROM table1
RIGHT JOIN table2
ON table1.common_field = table2.common_field;

Example

In this example, we are imitating the full join operation using UNION or UNION ALL keyword. First, let us create a table named CUSTOMERS using the following query −;

CREATE TABLE CUSTOMERS (
   ID INT NOT NULL,
   NAME VARCHAR (20) NOT NULL,
   AGE INT NOT NULL,
   ADDRESS CHAR (25),
   SALARY DECIMAL (18, 2),       
   PRIMARY KEY (ID)
);

Now insert values into this table using the INSERT statement as follows −

ID NAME AGE ADDRESS SALARY
1 Ramesh 32 Ahmedabad 2000.00
2 Khilan 25 Delhi 1500.00
3 Kaushik 23 Kota 2000.00
4 Chaitali 25 Mumbai 6500.00
5 Hardik 27 Bhopal 8500.00
6 Komal 22 Hyderabad 4500.00
7 Muffy 24 Indore 10000.00

Let us create another table ORDERS, containing the details of orders made and the date they are made on.

CREATE TABLE ORDERS (
   OID INT NOT NULL,
   DATE VARCHAR (20) NOT NULL,
   CUSTOMER_ID INT NOT NULL,
   AMOUNT DECIMAL (18, 2),
);

Using the INSERT statement, insert values into this table as follows −

INSERT INTO ORDERS VALUES 
(102, '2009-10-08 00:00:00', 3, 3000.00),
(100, '2009-10-08 00:00:00', 3, 1500.00),
(101, '2009-11-20 00:00:00', 2, 1560.00),
(103, '2008-05-20 00:00:00', 4, 2060.00);

The table is displayed as follows −

OID DATE CUSTOMER_ID AMOUNT
102 2009-10-08 00:00:00 3 3000.00
100 2009-10-08 00:00:00 3 1500.00
101 2009-11-20 00:00:00 2 1560.00
103 2008-05-20 00:00:00 4 2060.00

Full Join Query −

On executing the following query, we will produce the union of two tables CUSTOMERS and ORDERS.

SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
UNION
SELECT ID, NAME, AMOUNT, DATE
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID;

Output

The resultant table is produced as follows −

ID NAME AMOUNT DATE
1 Ramesh NULL NULL
2 Khilan 1560 2009-11-20 00:00:00
3 Kaushik 3000 2009-10-08 00:00:00
3 Kaushik 1500 2009-10-08 00:00:00
4 Chaitali 2060 2008-05-20 00:00:00
5 Hardik NULL NULL
6 Komal NULL NULL
7 Muffy NULL NULL

Full Join with WHERE Clause

With Joins, we are filtering records using the ON clause, by default. Let us suppose there is a further requirement to filter records based on a certain condition, we can make use of WHERE clause with the Joins.

Syntax

The syntax of Full Join when used with WHERE clause is given below −

SELECT column_name(s)
FROM table_name1
FULL JOIN table_name2
ON table_name1.column_name = table_name2.column_name
WHERE condition

Example

Consider the previous two tables CUSTOMERS and ORDERS, and join them using the following Full Join query by applying some constraints using the WHERE clause.

SELECT ID, NAME, DATE, AMOUNT 
FROM CUSTOMERS
LEFT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
WHERE ORDERS.AMOUNT > 2000.00

UNION 

SELECT ID, NAME, DATE, AMOUNT 
FROM CUSTOMERS
RIGHT JOIN ORDERS
ON CUSTOMERS.ID = ORDERS.CUSTOMER_ID
WHERE ORDERS.AMOUNT > 2000.00;

Output

The resultant table after applying the where clause with full join contains the rows that has amount values greater than 2000.00 −

ID NAME DATE AMOUNT
3 Kaushik 2009-10-08 00:00:00 3000.00
4 Chaitali 2008-05-20 00:00:00 2060.00
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