Joining tables in SQL allows you to combine rows from two or more tables into a single result set based on a related column between them. It is a powerful tool to combine data from multiple tables into a single result set. By using the JOIN clause, you can retrieve the desired columns from two or more tables based on a common column.

To join tables in SQL, you use the JOIN clause in your SELECT statement. The syntax is as follows:

SELECT column1, column2, ...
FROM table1
JOIN table2
ON table1.column = table2.column;

Where table1 and table2 are the names of the tables you want to join, ON clause specifies the condition that links the two tables based on a common column between them. The SELECT statement then defines which columns you want to retrieve from the joined tables.

There are four types of joins in SQL: INNER JOIN, LEFT JOIN (or LEFT OUTER JOIN), RIGHT JOIN (or RIGHT OUTER JOIN), and FULL OUTER JOIN. Each type returns a different subset of the joined data based on the matching records in each table.

INNER JOIN: Returns only the rows with matching values in both tables.

LEFT JOIN: Returns all the rows from the left table and the matching rows from the right table. If there’s no match, NULL values are displayed in the right table’s columns.

RIGHT JOIN: Returns all the rows from the right table and the matching rows from the left table. If there’s no match, NULL values are displayed in the left table’s columns.

FULL OUTER JOIN: Returns all the rows from both tables, including the unmatched rows. If there’s no match, NULL values are displayed in columns of the non-matching table.