Stop copying LogicalPlan and Exprs in PushDownFilter

Author: alamb

datafusion/expr/src/expr.rs

@@ -1275,6 +1275,28 @@ impl Expr {
         }
     }
 
+    /// Return a reference to the inner `Column` if any
+    ///
+    /// returns `None` if the expression is not a `Column`
+    ///
+    /// Example
+    /// ```
+    /// # use datafusion_common::Column;
+    /// use datafusion_expr::{col, Expr};
+    /// let expr = col("foo");
+    /// assert_eq!(expr.try_as_col(), Some(&Column::from("foo")));
+    ///
+    /// let expr = col("foo").alias("bar");
+    /// assert_eq!(expr.try_as_col(), None);
+    /// ```
+    pub fn try_as_col(&self) -> Option<&Column> {
+        if let Expr::Column(it) = self {
+            Some(it)
+        } else {
+            None
+        }
+    }
+
     /// Return all referenced columns of this expression.
     pub fn to_columns(&self) -> Result<HashSet<Column>> {
         let mut using_columns = HashSet::new();

datafusion/expr/src/logical_plan/plan.rs

@@ -2353,6 +2353,16 @@ pub enum Distinct {
     On(DistinctOn),
 }
 
+impl Distinct {
+    /// return a reference to the nodes input
+    pub fn input(&self) -> &Arc<LogicalPlan> {
+        match self {
+            Distinct::All(input) => input,
+            Distinct::On(DistinctOn { input, .. }) => input,
+        }
+    }
+}
+
 /// Removes duplicate rows from the input
 #[derive(Clone, PartialEq, Eq, Hash)]
 pub struct DistinctOn {