TJR Bootcamp Practice Test

Which JOIN type returns only matched rows from both tables?

FULL OUTER JOIN returns all rows from both tables regardless of matches. CROSS JOIN returns every possible combination of rows. INNER JOIN returns only matched rows from both tables. LEFT JOIN returns all rows from the right table and matched from the left.

Correct Answer:

INNER JOIN returns only matched rows from both tables.

Explanation:

When you want only the records that have matching values in both tables, you use an inner join. It returns the intersection of the two datasets based on the join condition, so a row appears only if there’s a corresponding row in the other table that satisfies the match. For example, joining customers and orders on customer_id yields customers who have placed orders, along with their order details, and excludes customers with no orders. The other join types behave differently: a full outer join brings in all rows from both tables, with NULLs where there’s no match; a cross join creates every possible pairing of rows (Cartesian product); a left join returns all rows from the left table and the matching rows from the right (and NULLs for the right side when there’s no match).

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