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A comment on What's new in the Postgres 16 query planner (a.k.a. optimizer). Parent comment

Re:What's new in the Postgres 16 query planner (a.k.a. optim... by davidrowley on Friday February 09, 2024 @08:33PM (#39322623)
UNION is certainly one way to eliminate the OR condition.

In theory, a hash join is possible with a condition like `ON t1.a = t2.a OR t1.b = t2.b`, but Hash Join would need to build two hash tables and only probe the 2nd one if the first lookup found nothing. I don't know if there are any RDBMSs that allow multiple hash tables in a hash join.

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Re:What's new in the Postgres 16 query planner (a.k.a. optim... by appplication on Friday February 09, 2024 @08:38PM (#39322662)
Yeah it feels like for some arbitrarily sized array contains join having something like a bloom filter involved could help reduce the search space. But I’m not a db engineer so perhaps the specific implementation details of that would turn out to make it a bad idea.
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