Which statement describes INNER JOIN behavior?

• A. INNER JOIN returns only rows with matching keys in both tables.
• B. INNER JOIN returns all rows from the left table with NULLs for non-matches in the right.
• C. INNER JOIN returns all rows from the right table with NULLs for non-matches in the left.
• D. INNER JOIN returns all combinations of rows from both tables.

Answer: (A)

Inner join brings together rows only when there is a matching value in both tables based on the join condition. In practice, that means you’ll see rows where the keys align; any row that doesn’t have a counterpart in the other table is excluded. If a row in one table matches multiple rows in the other, you’ll get multiple resulting rows—one for each match. For example, pairing customers with orders on customer_id gives one row per order for customers who placed orders, while customers with no orders don’t appear. This differs from a left join, which keeps all rows from the left table and fills in NULLs for non-matches on the right; a right join, the mirror opposite; and a cross join, which returns every possible combination of rows from both tables.