Which JOIN type returns all rows when there is a match in either side?

Which JOIN type returns all rows when there is a match in either side?

• A. INNER JOIN returns all rows when there is a match.
• B. FULL OUTER JOIN returns all rows when there is a match in either side.
• C. RIGHT JOIN returns all rows from the right table.
• D. LEFT JOIN returns all rows from the left table.

Answer: (B)

Preserving rows from both sides regardless of whether there’s a match is what the full outer join does. It brings back every row from both tables: if there is a matching row on the other side, the columns are combined; if there isn’t, the missing side’s columns appear as NULL. That means you get all rows that have a match on either side, plus any unmatched rows from either table. In contrast, inner joins keep only the rows where there is a match in both tables, left joins keep all rows from the left table (with NULLs for missing right-side data), and right joins do the same for the right table.

Preserving rows from both sides regardless of whether there’s a match is what the full outer join does. It brings back every row from both tables: if there is a matching row on the other side, the columns are combined; if there isn’t, the missing side’s columns appear as NULL. That means you get all rows that have a match on either side, plus any unmatched rows from either table. In contrast, inner joins keep only the rows where there is a match in both tables, left joins keep all rows from the left table (with NULLs for missing right-side data), and right joins do the same for the right table.