26 lines
971 B
Rust
26 lines
971 B
Rust
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//! Semijoin and natural join over binding relations.
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//!
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//! Both operators join on the shared column names of their inputs (the
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//! "overlapping variables" in Datalog terms).
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//!
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//! - [`semijoin`] keeps rows of `left` whose shared-column values appear in
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//! `right`. Output columns are `left.columns` unchanged.
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//! - [`natural_join`] keeps every pair `(l, r)` that agrees on shared columns,
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//! emitting one row with the union of columns. Output column order is
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//! `left.columns` followed by `right.columns` minus the shared ones.
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use crate::relation::Relation;
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#[must_use]
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pub fn semijoin(_left: &Relation, _right: &Relation) -> Relation {
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todo!("hash `right` on shared columns, probe with `left`, keep matching left rows")
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}
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#[must_use]
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pub fn natural_join(_left: &Relation, _right: &Relation) -> Relation {
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todo!(
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"hash one side on shared columns, probe with the other, emit \
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left ++ (right \\ shared) for every match"
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)
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}
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