3 ms·

hopefully you'll forgive my pedantry - "union all" is vertical concat - "union" without the "all" gives you the distinct list

• jhgb 4y ago
  One of the reasons why SQL is crap: there should be no distinction between the two in relational algebra. A set of {A, B, C, B, C} is the same as {A, B, C}.
  • 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 ago
      And not treating relationships as sets has costs of its own -- for example it breaks relational formula equivalences that could be used for query optimization.
  • intelijstupide 4y ago
  • SnowHill9902 4y ago
    For some definitions of same as.