Remove unnecessary DISTINCT ON expressions from introspection SQL.
#260
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**What:** There are two: 1. selecting only one relation per name 2. selecting only one aggregate function per input type These are both unnecessary. This work was inspired by CockroachDB failing to respect ordering within CTEs. **How:** The first, selecting only one relation per name, was there to avoid having to deal with multiple relations of the same name in distinct schemas, but we now support schemas (and prefix all relations with their schema name), so this is unnecessary and possibly dangerous. The second, selecting only one aggregate function per input type, is not necessary because we only support aggregate functions which take a single argument, and therefore there can only be one per input type _anyway_, i.e. you cannot have two aggregate functions of the same name with the same input type(s) and different return types (return type polymorphism) in PostgreSQL. We therefore simplify these queries to avoid having to use `DISTINCT ON` at all. Co-Authored-By: Philip Lykke Carlsen <[email protected]>
plcplc
approved these changes
Jan 18, 2024
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What
There are two:
These are both unnecessary.
This work was inspired by CockroachDB failing to respect ordering within CTEs.
How
The first, selecting only one relation per name, was there to avoid having to deal with multiple relations of the same name in distinct schemas, but we now support schemas (and prefix all relations with their schema name), so this is unnecessary and possibly dangerous.
The second, selecting only one aggregate function per input type, is not necessary because we only support aggregate functions which take a single argument, and therefore there can only be one per input type anyway, i.e. you cannot have two aggregate functions of the same name with the same input type(s) and different return types (return type polymorphism) in PostgreSQL.
We therefore simplify these queries to avoid having to use
DISTINCT ONat all.