jackwener commented on code in PR #8312:
URL: https://github.com/apache/arrow-datafusion/pull/8312#discussion_r1413698745
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datafusion/expr/src/logical_plan/plan.rs:
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@@ -1935,6 +1942,73 @@ impl Filter {
Ok(Self { predicate, input })
}
+
+ /// Is this filter guaranteed to return 0 or 1 row in a given
instantiation?
+ ///
+ /// This function will return `true` if its predicate contains a
conjunction of
+ /// `col(a) = <expr>`, where its schema has a unique filter that is covered
+ /// by this conjunction.
+ ///
+ /// For example, for the table:
+ /// ```sql
+ /// CREATE TABLE t (a INTEGER PRIMARY KEY, b INTEGER);
+ /// ```
+ /// `Filter(a = 2).is_scalar() == true`
+ /// , whereas
+ /// `Filter(b = 2).is_scalar() == false`
+ /// and
+ /// `Filter(a = 2 OR b = 2).is_scalar() == false`
+ fn is_scalar(&self) -> bool {
Review Comment:
Yes, and add these definition into doc/
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