What is the usage of JOIN in a database?

JOIN is an operation used to connect two or more tables based on their relationships. It is used to retrieve relevant data and combine them into a single result set. JOIN operations typically rely on common columns between tables, where these columns have the same values in each table.

The syntax for a JOIN operation is typically as follows:

SELECT column_name
FROM table1
JOIN table2 ON table1.column = table2.column

The JOIN keyword in this syntax is used to specify the way tables are connected and the columns to be connected. The ON keyword is used to specify the conditions for the connection.

There are different types of JOIN operations, which include:

1. INNER JOIN: Returns rows that have matching values in both tables. Only rows with the same values in the join columns are included in the results.
2. LEFT JOIN: Returns all rows from the left table, as well as any matching rows from the right table. If there are no matching rows from the right table, the result will include NULL values.
3. RIGHT JOIN: Returns all rows from the right table, as well as the rows from the left table that match the rows in the right table. If there are no matching rows in the left table, NULL values will be included in the result.
4. FULL JOIN: Returns all rows from both the left and right tables. If there is no match for a row in either table, the result will include NULL values.

The JOIN operation can be nested as needed and it can be used to connect multiple tables. By using the JOIN operation, data can be efficiently retrieved and combined from multiple tables to meet specific query requirements.