0.57.0 (2024-10-02)
⚠ BREAKING CHANGES
- This PR changes the definition of grouping sets in
AggregateRelto consist of references into a list of grouping
expressions instead of consisting of expressions directly.
With the previous definition, consumers had to deduplicate the
expressions in the grouping sets in order to execute the query or even
derive the output schema (which is problematic, as explained below).
With this change, the responsibility of deduplicating expressions is now
on the producer. Concretely, consumers are now expected to be simpler:
The list of grouping expressions immediately provides the information
needed to derive the output schema and the list of grouping sets
explicitly and unambiguously provides the equality of grouping
expressions. Producers now have to specify the grouping sets explicitly.
If their internal representation of grouping sets consists of full
grouping expressions (rather than references), then they must
deduplicate these expressions according to their internal notion of
expression equality in order to produce grouping sets consisting of
references to these deduplicated expressions.
If the previous format is desired, it can be obtained from the new
format by (1) deduplicating the grouping expressions (according to the
previously applicable definition of expression equality), (2)
re-establishing the duplicates using the emit clause, and (3)
"dereferencing" the references in the grouping sets, i.e., by replacing
each reference in the grouping sets with the expression it refers to.
The previous version was problematic because it required the consumers
to deduplicate the expressions from the grouping sets. This, in turn,
requires to parse and understand 100% of these expression even in cases
where that understanding is otherwise optional, which is in opposition
to the general philosophy of allowing for simple-minded consumers. The
new version avoids that problem and, thus, allows consumers to be