feat: ProjectionDropOut optimizer

Author: gandronchik

datafusion/core/src/logical_plan/expr_rewriter.rs

@@ -465,6 +465,32 @@ pub fn replace_col(e: Expr, replace_map: &HashMap<&Column, &Column>) -> Result<E
     e.rewrite(&mut ColumnReplacer { replace_map })
 }
 
+/// Recursively replace all Column expressions in a given expression tree with Expressions
+/// provided by the hash map argument.
+pub fn replace_col_to_expr(
+    e: Expr,
+    replace_map: &HashMap<&Column, &Expr>,
+) -> Result<Expr> {
+    struct ColumnReplacer<'a> {
+        replace_map: &'a HashMap<&'a Column, &'a Expr>,
+    }
+
+    impl<'a> ExprRewriter for ColumnReplacer<'a> {
+        fn mutate(&mut self, expr: Expr) -> Result<Expr> {
+            if let Expr::Column(c) = &expr {
+                match self.replace_map.get(c) {
+                    Some(new_e) => Ok((*new_e).to_owned()),
+                    None => Ok(expr),
+                }
+            } else {
+                Ok(expr)
+            }
+        }
+    }
+
+    e.rewrite(&mut ColumnReplacer { replace_map })
+}
+
 /// Recursively 'unnormalize' (remove all qualifiers) from an
 /// expression tree.
 ///

datafusion/core/src/logical_plan/mod.rs

@@ -55,9 +55,9 @@ pub use expr::{
     trunc, unalias, upper, when, Column, Expr, ExprSchema, Like, Literal,
 };
 pub use expr_rewriter::{
-    normalize_col, normalize_cols, replace_col, rewrite_sort_cols_by_aggs,
-    rewrite_udtfs_to_columns, unnormalize_col, unnormalize_cols, ExprRewritable,
-    ExprRewriter, RewriteRecursion,
+    normalize_col, normalize_cols, replace_col, replace_col_to_expr,
+    rewrite_sort_cols_by_aggs, rewrite_udtfs_to_columns, unnormalize_col,
+    unnormalize_cols, ExprRewritable, ExprRewriter, RewriteRecursion,
 };
 pub use expr_schema::ExprSchemable;
 pub use expr_simplier::{ExprSimplifiable, SimplifyInfo};
@@ -66,8 +66,8 @@ pub use extension::UserDefinedLogicalNode;
 pub use operators::Operator;
 pub use plan::{
     CreateCatalogSchema, CreateExternalTable, CreateMemoryTable, CrossJoin, Distinct,
-    DropTable, EmptyRelation, JoinConstraint, JoinType, Limit, LogicalPlan, Partitioning,
-    PlanType, PlanVisitor, Repartition, StringifiedPlan, Subquery, TableScan,
-    ToStringifiedPlan, Union, Values,
+    DropTable, EmptyRelation, Filter, JoinConstraint, JoinType, Limit, LogicalPlan,
+    Partitioning, PlanType, PlanVisitor, Repartition, StringifiedPlan, Subquery,
+    TableScan, ToStringifiedPlan, Union, Values,
 };
 pub use registry::FunctionRegistry;

datafusion/core/src/optimizer/mod.rs

@@ -25,6 +25,7 @@ pub mod eliminate_limit;
 pub mod filter_push_down;
 pub mod limit_push_down;
 pub mod optimizer;
+pub mod projection_drop_out;
 pub mod projection_push_down;
 pub mod simplify_expressions;
 pub mod single_distinct_to_groupby;