What are the Differences Between MySQL's INNER, LEFT, RIGHT, and FULL Joins?

MySQL Joins: Types and Differences Explained

In MySQL, joins play a crucial role in combining data from multiple tables. Various join types exist, providing different methods to retrieve data based on specific criteria. This article breaks down the key differences among these joins.

Commented-Separated Join

The comma-separated join, as you mentioned, is also known as the implicit join. It uses the comma operator (",") to list multiple tables in the FROM clause. For instance:

SELECT * FROM a, b WHERE b.id = a.beeId AND ...

INNER JOIN

The INNER JOIN, denoted by the ON keyword, retrieves rows only when a match exists in both tables. It matches rows based on the specified equality condition, returning only those rows that have corresponding values in both tables.

LEFT JOIN

LEFT JOIN, also called LEFT OUTER JOIN, retrieves all rows from the left table, even if they don't have a matching row in the right table. This means it includes rows from the left table that have no corresponding rows in the right table.

RIGHT JOIN

RIGHT JOIN, or RIGHT OUTER JOIN, retrieves all rows from the right table, even if they don't have a matching row in the left table. Similar to LEFT JOIN, it includes rows from the right table that have no corresponding rows in the left table.

FULL JOIN

FULL JOIN, also known as FULL OUTER JOIN, returns rows that have a match in either the left or right table. It combines the results of INNER JOIN and LEFT JOIN or RIGHT JOIN, displaying all rows from both tables, regardless of whether they have a match.

SET Differences

• LEFT JOIN: Includes left table rows without matches in the right table.
• RIGHT JOIN: Includes right table rows without matches in the left table.
• INNER JOIN: Excludes rows that have no matching row in both tables.
• FULL JOIN: Includes all rows from both tables, even if they have no matching row in the other table.

To summarize, each join type has its unique purpose. Comma-separated and implicit joins have similar behavior, while explicit joins (INNER, LEFT, RIGHT, FULL) provide more granular control over the retrieval of data based on the desired search criteria.

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