One example is that in Presto, joins assume that left (IIRC) table is the big on... | Hacker News

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Scene_Cast2 on April 14, 2024 | parent | context | favorite | on: Show HN: PostgreSQL index advisor

One example is that in Presto, joins assume that left (IIRC) table is the big one you stream, and the right one is the small one you hash. One of the newer features was that in some cases, the optimizer is able to ignore the SQL order and correctly pick which table to hash and which one to stream.

legulere on April 14, 2024 [–]

Isn't that just basic table/index statistics to know which table is the smallest?

Scene_Cast2 on April 15, 2024 | [–]

Not if you're joining on a filtered table or a result of another join.

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