3 ms·
Detecting duplicates has a cost you can't just hand-wave away. UNION ALL tells the engine not to worry about it and just output as it sees it, usually going fas
by ttfkam 4y ago
Detecting duplicates has a cost you can't just hand-wave away. UNION ALL tells the engine not to worry about it and just output as it sees it, usually going faster. Depends on your data needs.
- jhgb 4y agoAnd not treating relationships as sets has costs of its own -- for example it breaks relational formula equivalences that could be used for query optimization.