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by hn_throwaway_99
1060 days ago
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Completely agree, thanks for putting it better than I could have, with an excellent example. Correlated subqueries like the example you give, or similarly lateral joins in postgres, fundamentally are treated like for loops by DB engines anyway. Semi-related, but the example you give is also why I love Postgres' "DISTINCT ON" functionality (I don't know if other DBs have something similar) - it makes it so much easier to reason about these "give me the 'first' one from each group" type queries without having to resort to correlated subqueries. |
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