What is the difference between inner and outer join in SQL?

What is the difference between inner and outer join in SQL?

Approach: Compare row inclusion based on matches.

Inner join returns only rows where there is a match in both tables. Outer join (Left, Right, or Full) returns matched rows and unmatched rows from one or both tables, filling missing values with NULL.

Follow-up: What is a cross join?

Key concepts: intersection, null values, table matching.