alamb commented on code in PR #18848:
URL: https://github.com/apache/datafusion/pull/18848#discussion_r2547230624
##########
datafusion/optimizer/src/push_down_filter.rs:
##########
@@ -418,6 +418,204 @@ fn extract_or_clause(expr: &Expr, schema_columns:
&HashSet<Column>) -> Option<Ex
predicate
}
+/// Tracks coalesce predicates that can be pushed to each side of a FULL JOIN.
+struct PushDownCoalesceFilterHelper {
+ join_keys: Vec<(Column, Column)>,
+ left_filters: Vec<Expr>,
+ right_filters: Vec<Expr>,
+ remaining_filters: Vec<Expr>,
+}
+
+impl PushDownCoalesceFilterHelper {
+ fn new(join_keys: &[(Expr, Expr)]) -> Self {
+ let join_keys = join_keys
+ .iter()
+ .filter_map(|(lhs, rhs)| {
+ Some((lhs.try_as_col()?.clone(), rhs.try_as_col()?.clone()))
+ })
+ .collect();
+ Self {
+ join_keys,
+ left_filters: Vec::new(),
+ right_filters: Vec::new(),
+ remaining_filters: Vec::new(),
+ }
+ }
+
+ fn push_columns<F: FnMut(Expr) -> Expr>(
+ &mut self,
+ columns: (Column, Column),
+ mut build_filter: F,
+ ) {
+ self.left_filters
+ .push(build_filter(Expr::Column(columns.0)));
+ self.right_filters
+ .push(build_filter(Expr::Column(columns.1)));
+ }
+
+ fn extract_join_columns(&self, expr: &Expr) -> Option<(Column, Column)> {
+ if let Expr::ScalarFunction(ScalarFunction { func, args }) = expr {
+ if func.name() != "coalesce" {
Review Comment:
this seems very specific to coalesce and will likely break anyone who
provides their own implementation of `coalesce` that overrides the built in one
Can we formualte this as some more general property of the function that
allows pushing down? That way we could mark coalesce as having this property
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