alamb commented on code in PR #10948:
URL: https://github.com/apache/datafusion/pull/10948#discussion_r1642553216
##########
datafusion/optimizer/src/push_down_filter.rs:
##########
@@ -785,7 +782,7 @@ impl OptimizerRule for PushDownFilter {
let mut keep_predicates = vec![];
let mut push_predicates = vec![];
for expr in predicates {
- let cols = expr.to_columns()?;
+ let cols = expr.column_refs();
Review Comment:
This is a pretty good example where there is no need to copy `Column`s
simply to check if they are referenced.
##########
datafusion/expr/src/expr.rs:
##########
@@ -1333,6 +1335,46 @@ impl Expr {
Ok(using_columns)
}
+ /// Return all references to columns in this expression.
+ ///
+ /// # Example
+ /// ```
+ /// # use std::collections::HashSet;
+ /// # use datafusion_common::Column;
+ /// # use datafusion_expr::col;
+ /// // For an expression `a + (b * a)`
+ /// let expr = col("a") + (col("b") * col("a"));
+ /// let refs = expr.column_refs();
+ /// // refs contains "a" and "b"
+ /// assert_eq!(refs.len(), 2);
+ /// assert!(refs.contains(&Column::new_unqualified("a")));
+ /// assert!(refs.contains(&Column::new_unqualified("b")));
+ /// ```
+ pub fn column_refs(&self) -> HashSet<&Column> {
Review Comment:
The implementation of this function is quite nice now compared to the
`expr_to_columns` one:
https://github.com/alamb/datafusion/blob/58d0c34d77c9a5202e62b9281cdbf1046abaa096/datafusion/expr/src/utils.rs#L264-L309
##########
datafusion/expr/src/utils.rs:
##########
@@ -46,6 +46,7 @@ pub const COUNT_STAR_EXPANSION: ScalarValue =
ScalarValue::Int64(Some(1));
/// Recursively walk a list of expression trees, collecting the unique set of
columns
/// referenced in the expression
+#[deprecated(since = "40.0.0", note = "Expr::add_column_refs instead")]
Review Comment:
this function is not used anywhere in the datafusion codebase
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