Explain joins in SQL.

In SQL, a join combines rows from two or more tables based on a related column. The most common types are:

• INNER JOIN: returns rows where the join condition is true in both tables.
• LEFT (OUTER) JOIN: returns all rows from the left table and matching rows from the right; unmatched right rows are NULL.
• RIGHT (OUTER) JOIN: opposite of LEFT.
• FULL (OUTER) JOIN: returns rows when there is a match in either table.
• CROSS JOIN: returns the Cartesian product of the two tables.
• SELF JOIN: a table joined to itself, useful for hierarchical data.

Example: SELECT e.name, d.name FROM employees e JOIN departments d ON e.dept_id = d.id; This returns employee names with their department names where dept_id matches. Joins are fundamental for relational data retrieval and enable complex queries across multiple tables.