AssHero commented on code in PR #3578:
URL: https://github.com/apache/arrow-datafusion/pull/3578#discussion_r994355657
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datafusion/optimizer/src/filter_push_down.rs:
##########
@@ -248,6 +249,145 @@ fn get_pushable_join_predicates<'a>(
.unzip()
}
+// examine OR clause to see if any useful clauses can be extracted and push
down.
+// extract at least one qual of each sub clauses of OR clause, then form the
quals
+// to new OR clause as predicate.
+//
+// Filter: (a = c and a < 20) or (b = d and b > 10)
+// join/crossjoin:
+// TableScan: projection=[a, b]
+// TableScan: projection=[c, d]
+//
+// is optimized to
+//
+// Filter: (a = c and a < 20) or (b = d and b > 10)
+// join/crossjoin:
+// Filter: (a < 20) or (b > 10)
+// TableScan: projection=[a, b]
+// TableScan: projection=[c, d]
+//
+// In general, predicates of this form:
+//
+// (A AND B) OR (C AND D)
+//
+// will be transformed to
+//
+// ((A AND B) OR (C AND D)) AND (A OR C)
+//
+// OR
+//
+// ((A AND B) OR (C AND D)) AND ((A AND B) OR C)
+//
+// OR
+//
+// do nothing.
+//
+fn extract_or_clauses_for_join(
+ filters: &[&Expr],
+ schema: &DFSchema,
+ preserved: bool,
+) -> (Vec<Expr>, Vec<HashSet<Column>>) {
+ if !preserved {
+ return (vec![], vec![]);
+ }
+
+ let schema_columns = schema
+ .fields()
+ .iter()
+ .flat_map(|f| {
+ [
+ f.qualified_column(),
+ // we need to push down filter using unqualified column as well
+ f.unqualified_column(),
+ ]
+ })
+ .collect::<HashSet<_>>();
+
+ let mut exprs = vec![];
+ let mut expr_columns = vec![];
+ for expr in filters.iter() {
+ if let Expr::BinaryExpr {
+ left,
+ op: Operator::Or,
+ right,
+ } = expr
+ {
+ let left_expr = extract_or_clause(left.as_ref(), &schema_columns);
+ let right_expr = extract_or_clause(right.as_ref(),
&schema_columns);
+
+ // If nothing can be extracted from any sub clauses, do nothing
for this OR clause.
+ if let (Some(left_expr), Some(right_expr)) = (left_expr,
right_expr) {
+ let predicate = or(left_expr, right_expr);
+ let mut columns: HashSet<Column> = HashSet::new();
+ expr_to_columns(&predicate, &mut columns).ok().unwrap();
+
+ exprs.push(predicate);
+ expr_columns.push(columns);
+ }
+ }
+ }
+
+ (exprs, expr_columns)
+}
+
+// extract qual from OR sub-clause.
Review Comment:
sure, I can add more comments for this.
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