Choosing UNION or JOIN for a real scenario

Question

Accepted Answer

When two tables share the same column structure and you want all rows from both in one list, UNION is exactly right. It stacks the rows vertically - each row still has name and email, just sourced from different tables. A JOIN would try to match rows between the two tables using a condition, producing columns from both tables side by side - not what we want here. Use UNION ALL instead of UNION if you expect no duplicates (or want them), since UNION pays the cost of deduplication.