Which SQL operator allows combining the results of two or more SELECT queries into a single result set?

Which SQL operator allows combining the results of two or more SELECT queries into a single result set?

• A. JOIN
• B. UNION ALL
• C. MERGE
• D. UNION

Answer: (D)

Combining results from multiple SELECT queries into one output uses a set operation. The operator that does this by taking the results of the queries and returning a single combined set is UNION. It stitches the rows together and, by default, removes any duplicates, giving you the distinct rows that appear across all queries. If you need to keep duplicates, UNION ALL will preserve them, producing a single set as well but with repeated rows. Understanding the others helps place this in context: JOIN brings together rows from two sources side by side based on a related column, resulting in more columns rather than more rows. MERGE is a data manipulation operation used to insert, update, or delete rows in a target table based on a source, not simply to concatenate results. So UNION is the right tool when the goal is to combine the results of separate queries into a single result set.

Combining results from multiple SELECT queries into one output uses a set operation. The operator that does this by taking the results of the queries and returning a single combined set is UNION. It stitches the rows together and, by default, removes any duplicates, giving you the distinct rows that appear across all queries. If you need to keep duplicates, UNION ALL will preserve them, producing a single set as well but with repeated rows.

Understanding the others helps place this in context: JOIN brings together rows from two sources side by side based on a related column, resulting in more columns rather than more rows. MERGE is a data manipulation operation used to insert, update, or delete rows in a target table based on a source, not simply to concatenate results. So UNION is the right tool when the goal is to combine the results of separate queries into a single result set.