Union Datasets — Solution & ExplanationProblems / Union Datasets / EditorialApproachUNION ALL combines the rows from two queries into one result set.

SELECT ... FROM online_orders with 'online' AS source tags each row.

UNION ALL appends the second query's rows.

SELECT ... FROM store_orders with 'store' AS source tags store rows.

ORDER BY order_date sorts the combined result.

UNION ALL keeps all rows including duplicates. UNION (without ALL) would deduplicate, which is rarely what you want.Hints

UNION ALL stacks two result sets on top of each other.

Both SELECTs must have the same number of columns with compatible types.

Use a string literal like 'online' AS source to add a tag column.