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 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 join to table B. Here 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 of Left Join vs Right Join
Given below are the key differences of 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. Below syntax can be used to neglect the NULL values:
SELECT * FROM TABLE_A A |
The result set contains NULL set values. Below syntax can be used to neglect the NULL values:
SELECT * FROM TABLE_A A |
| 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.
- ON keyword is used to specify the condition and join the tables.
Examples to Implement Left Outer Join
Below is the example to implement 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. 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 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 the right table and the Borrower is the left table. As in left OUTER join, we get inner join+ all rows from the left table. Here we get all the rows from the Borrower table which is left the table and inner join rows with the loan table. Values not present will be NULL.
Conclusion
To fetch data relevant to the customer requirement we might need to join tables which will be fulfilled by joins. As mentioned earlier joins are used to get data from more than one table. To join more than one table we need at least one column common in both tables. Tables get joined based on the condition specified.
Recommended Articles
This is a guide to Left Outer Join in MySQL. Here we discuss how to use left outer join? with key difference between left and right joins along with examples to implement. You can also go through our other related articles to learn more –
