SQL
All Top 50 SQL Interview Questions#40
UNION vs UNION ALL Performance and Set Semantics in SQL
EasyInterview Question #40
Combine candidate applications from `domestic_applications` and `international_applications`. Explain when `UNION ALL` is preferred over `UNION`.
Input Table: domestic & international
2 rows preview| candidate_id | |
|---|---|
| 1 | amit@gmail.com |
| 2 | john@gmail.com |
Expected Output Structure2 rows
| candidate_id | |
|---|---|
| 1 | amit@gmail.com |
| 2 | john@gmail.com |
Interview Context
Asked frequently in data analyst and business analyst technical rounds. Focus on clean filtering, optimal indexing usage, and unambiguous column selection.
PostgreSQL 15
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