Give me a brief on how a SQL join works.

A SQL 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, filling missing values with NULL; Right Join – the opposite of left; Full Outer Join – returns all rows from both tables, NULL where there is no match; Cross Join – returns the Cartesian product of the two tables. The join condition is typically an equality on key columns, but can include inequalities or complex expressions. Joins are implemented by the query optimizer using hash, merge, or nested loop algorithms depending on indexes, data size, and statistics. Understanding join types is essential for writing correct queries and optimizing performance.