Left Outer Join in MySQL

Updated May 10, 2023

Introduction to Left Outer Join in MySQL

In this article, we will see about the Left Outer Join in MySQL. Left Outer Join gets all the rows from the left table and the common rows of both tables.

Let us take an example of the right join.

Example:

Below represents the Venn diagram of the left outer join.

In the below diagram, Table A is left joined to Table B. Here are all the rows from the table. A gets considered, and common rows from both tables.

Syntax:

SELECT * FROM TABLE_A A
LEFT OUTER JOIN TABLE_B B
ON A.Common_COLUMN=B.Common_COLUMN
WHERE <Condition>

Key Differences between Left Join vs Right Join

Given below are the key differences between left join vs right join:

Left Outer Join	Right Outer Join
Consider all the rows from the table and common rows from both tables.	Consider all rows from the right table and common from both tables.
INNER Join + all rows from the left table.	INNER Join + all rows from the right table.
Joins based on a condition.	Joins based on a condition.
ON keyword is used to specify the condition and join the tables.	ON keyword is used to specify the condition and join the tables.
The result set contains NULL set values. The below syntax can be used to neglect the NULL values: SELECT * FROM TABLE_A A LEFT OUTER JOIN TABLE B B ON A. Common_COLUMN =B. Common_COLUMN WHERE B.Common_COLUMN IS NULL	The result set contains NULL set values. The below syntax can be used to neglect the NULL values: SELECT * FROM TABLE_A A RIGHT OUTER JOIN TABLE B B ON A. Common_COLUMN =B. Common_COLUMN WHERE A.Common_COLUMN IS NULL
SELECT * FROM TABLE_A LEFT OUTER JOIN TABLE B ON A. Common_COLUMN =B. Common_COLUMN	SELECT * FROM TABLE_A RIGHT OUTER JOIN TABLE B ON A. Common_COLUMN =B. Common_COLUMN

How to use LEFT Outer Join in MYSQL?

• LEFT Outer Join = All rows from LEFT table + INNER Join.
• Consider all rows from the left table and common from both tables.
• Joins based on a condition.
• You can use the ON keyword to specify the condition and join the tables.

Examples to Implement Left Outer Join

Below is an example of implementing Left Outer Join in MySQL:

Example #1

Let us consider two tables and apply LEFT Outer join on the tables:

Loan Table:

Borrower:

Query to get the loan_no, status, and borrower date from two tables:

Code:

SELECT L.LOAN_NO, L.LOAN_STATUS, B.BORROWER_DATE
FROM LOAN L LEFT OUTER JOIN BORROWER B
ON L.LOAN_NO=B.LOAN_NO

Let’s check the output of the above table after applying the left outer join on them.

Output:

The result set contains NULL set values. The below syntax can be used to neglect the NULL values:

Code:

SELECT * FROM TABLE_A A
LEFT OUTER JOIN TABLE B B
ON A. Common_COLUMN =B. Common_COLUMN
WHERE A.Common_COLUMN IS NULL

Example #2

Let us consider two tables and apply LEFT outer join on the tables: Query to get the loan_no, status, loan_aount, and borrower date from two tables.

Code: 

SELECT L.LOAN_NO, L.LOAN_STATUS,L.LOAN_AMOUNT, B.BORROWER_DATE
FROM LOAN L LEFT OUTER JOIN BORROWER B
ON L.LOAN_NO=B.LOAN_NO

Let’s check the output of the above table after applying the left outer join on them.

Output:

Example #3

Let us consider two tables and apply the Left outer join on the tables: Query to get the loan_no, status, loan_amount, and borrower date from two tables.

Code:

SELECT L.LOAN_NO, L.LOAN_STATUS,L.LOAN_AMOUNT, B.BORROWER_DATE
FROM BORROWER B LEFT OUTER JOIN LOAN L
ON L.LOAN_NO=B.LOAN_NO

Let’s check the output of the above table after applying the left outer join on them.

Output:

In the above table, LOAN is on the right table, and the borrower is on the left. As in left OUTER join, we get inner join+ all rows from the left table. We left join the Borrower table with the Loan table to get all the rows from the Borrower table and inner join the rows. Values not present will be NULL.

Conclusion

To fetch data relevant to the customer requirement, we might need to join tables that will fulfill. As mentioned earlier, joins are used to get data from multiple tables. To join more than one table, we need at least one column common in both tables. Tables get joined based on the condition specified.

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