wip: pushdown mfp

src/expr/src/linear.rs

@@ -146,6 +146,11 @@ impl MapFilterProject {
         self
     }
 
+    pub fn apply(self, other: &MapFilterProject) -> MapFilterProject {
+        let (m, f, p) = other.as_map_filter_project();
+        self.map(m).filter(f).project(p)
+    }
+
     /// As the arguments to `Map`, `Filter`, and `Project` operators.
     ///
     /// In principle, this operator can be implemented as a sequence of
@@ -161,6 +166,10 @@ impl MapFilterProject {
         (map, filter, project)
     }
 
+    pub fn arity(&self) -> usize {
+        self.projection.len()
+    }
+
     /// Optimize the internal expression evaluation order.
     pub fn optimize(&mut self) {
         // This should probably resemble existing scalar cse.

src/expr/src/relation/mod.rs

@@ -507,17 +507,25 @@ impl RelationExpr {
 
     /// Retains only the columns specified by `output`.
     pub fn project(self, outputs: Vec<usize>) -> Self {
-        RelationExpr::Project {
-            input: Box::new(self),
-            outputs,
+        if outputs.len() == self.arity() && outputs.iter().enumerate().all(|(i, j)| i == *j) {
+            self
+        } else {
+            RelationExpr::Project {
+                input: Box::new(self),
+                outputs,
+            }
         }
     }
 
     /// Append to each row the results of applying elements of `scalar`.
     pub fn map(self, scalars: Vec<ScalarExpr>) -> Self {
-        RelationExpr::Map {
-            input: Box::new(self),
-            scalars,
+        if scalars.is_empty() {
+            self
+        } else {
+            RelationExpr::Map {
+                input: Box::new(self),
+                scalars,
+            }
         }
     }
 
@@ -536,9 +544,14 @@ impl RelationExpr {
     where
         I: IntoIterator<Item = ScalarExpr>,
     {
-        RelationExpr::Filter {
-            input: Box::new(self),
-            predicates: predicates.into_iter().collect(),
+        let preds: Vec<ScalarExpr> = predicates.into_iter().collect();
+        if preds.is_empty() {
+            self
+        } else {
+            RelationExpr::Filter {
+                input: Box::new(self),
+                predicates: preds,
+            }
         }
     }
 

src/transform/Cargo.toml

@@ -12,5 +12,5 @@ itertools = "0.9"
 repr = { path = "../repr" }
 
 [dev-dependencies]
-datadriven = "0.3.0"
+datadriven = "0.4.0"
 anyhow = "1.0.33"

src/transform/src/lib.rs

@@ -36,6 +36,7 @@ pub mod inline_let;
 pub mod join_elision;
 pub mod join_implementation;
 pub mod map_lifting;
+pub mod mfp_pushdown;
 pub mod nonnull_requirements;
 pub mod nonnullable;
 pub mod predicate_pushdown;