SQL JOIN is a powerful operation that combines data from multiple tables in a database based on a specified relationship between them. It’s like merging different pieces of information to create a comprehensive view. There are different types of joins, each serving a unique purpose:
INNER JOIN
This type returns only the rows where there is a match between the specified columns in both tables. It’s like getting a list of students who are also club members.
LEFT JOIN (or LEFT OUTER JOIN)
This returns all rows from the left table and the matching rows from the right table. NULL values are returned if there’s no match in the right table. It’s like listing all students and their club memberships, even if some aren’t in a club.
RIGHT JOIN (or RIGHT OUTER JOIN)
Similar to the LEFT JOIN, it returns all rows from the right table and the matching rows from the left table. It’s like listing all club memberships and the students who are part of them.
FULL OUTER JOIN
This returns all rows from both tables, with NULL values in places where there’s no match. It’s like combining a list of all students and a list of all club memberships, showing both who’s in a club and who isn’t.
CROSS JOIN (or CARTESIAN JOIN)
This generates a cartesian product of two tables, meaning every row from the left table is paired with every row from the right table. It’s like making all possible combinations of students and clubs, even if they don’t match.
If you wish to learn more about how SQL works in databases, please visit this post.
