Remove superfluous DISTINCT #2561
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Angeber. |
Bouncner
reviewed
May 10, 2023
| @@ -103,6 +91,34 @@ void DependentGroupByReductionRule::_apply_to_plan_without_subqueries( | |||
| }; | |||
| auto group_by_columns = fetch_group_by_columns(); | |||
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| // Early exit (i): If this is an AggregateNode for SELECT DISTINCT (i.e., it has no aggregates) and the requested | |||
| // columns are already distinct, remove the whole node. | |||
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entire?
Could you elaborate a little bit more here?
- Why do we replace an aggregate with a projection?
- Why do we use the group by count? Why does it need to be the same? (maybe explain for
select distinct name from lineitem;?)
I would have expected to see something with "DISTINCT" here.
src/test/lib/optimizer/strategy/dependent_group_by_reduction_rule_test.cpp
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src/lib/optimizer/strategy/dependent_group_by_reduction_rule.hpp
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src/test/lib/optimizer/strategy/dependent_group_by_reduction_rule_test.cpp
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@Bouncner better? |
Bouncner
approved these changes
May 16, 2023
nikriek
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Oct 28, 2023
Implements a pattern that removes the DISTINCT clause if the result is unique by definition or previous GROUP BY clauses.
nikriek
pushed a commit
that referenced
this pull request
Nov 6, 2023
Implements a pattern that removes the DISTINCT clause if the result is unique by definition or previous GROUP BY clauses.
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Thanks to @Bouncner, I read the following note in a paper:
That's true and it does not look like they will even merge it soon: https://commitfest.postgresql.org/35/2433/
Thus, I was triggered to implement it in Hyrise and prove we can do this in less than half an hour. It does not change anything in benchmarks, but now, we have it.
(To be fair: The Postgres contributors had to implement passing UCCs in the LQP and tried multiple versions. Also, I needed more than half an hour with all tests and an edge case I forgot to cover.)