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Difference Between Truncate/Delete and Union/Union All – Performance and Usage

SQLhard0.5 min readPremium
Frequency
Low
Asked at 1 company
Category
487
questions in SQL
Difficulty Split
130E|271M|86H
in this category
Total Bank
1,863
across 7 categories
Asked at these companies
Presidio
Key Concepts Tested
etlspark
Expert AnswerPremium
100 wordsInterview-ready
**Architectural Logic**: TRUNCATE vs DELETE and UNION vs UNION ALL have semantic and performance implications. **TRUNCATE vs DELETE**: TRUNCATE = metadata-only, fast, no WHERE, no rollback. DELETE = row-level, supports WHERE, rollback, slower. Use TRUNCATE for full refresh; DELETE for selective removal. **UNION vs UNION ALL**: UNION = deduplicates (implicit sort/distinct); slower. UNION ALL = keeps all rows; faster. Use UNION when dedup required; UNION ALL when impossible or acceptable....
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