MySQL Left Join vs Right Join

The MySQL LEFT JOIN and RIGHT JOIN are types of join operations used to combine rows from two or more tables based on a specified condition. These two types of joins are used to retrieve data from related tables, but they differ in how they handle unmatched rows from the tables involved in the join. Here’s an explanation of each:

LEFT JOIN:

• A LEFT JOIN, also known as a LEFT OUTER JOIN, returns all rows from the left (first) table and the matched rows from the right (second) table. If there is no match in the right table, the result will contain NULL values for columns from the right table.
• In a LEFT JOIN, the left table is the table that appears before the LEFT JOIN keyword, and the right table appears after it.
• LEFT JOIN is commonly used when you want to retrieve all rows from the left table along with matching rows from the right table. It ensures that no data is left out from the left table, even if there are no corresponding records in the right table.

Syntax for LEFT JOIN:

SELECT columns
FROM left_table
LEFT JOIN right_table ON left_table.column = right_table.column;

RIGHT JOIN:

• A RIGHT JOIN, also known as a RIGHT OUTER JOIN, returns all rows from the right (second) table and the matched rows from the left (first) table. If there is no match in the left table, the result will contain NULL values for columns from the left table.
• In a RIGHT JOIN, the right table is the table that appears before the RIGHT JOIN keyword, and the left table appears after it.
• RIGHT JOIN is used less frequently than LEFT JOIN. It is essentially a LEFT JOIN with the order of the tables reversed.

Syntax for RIGHT JOIN:

SELECT columns
FROM left_table
RIGHT JOIN right_table ON left_table.column = right_table.column;

In summary:

• Use a LEFT JOIN when you want all records from the left table and only matching records from the right table. It ensures that no data from the left table is omitted.
• Use a RIGHT JOIN when you want all records from the right table and only matching records from the left table. It is less commonly used, and many developers prefer to express the same logic using a LEFT JOIN with the tables swapped.
• The choice between LEFT JOIN and RIGHT JOIN depends on the specific requirements of your query and which table you consider as the primary table in the join.