Delete redundant joins by substitution equi-join keys for their mirror to render one side pruneable

demos/notebooks/4_tpch.ipynb

@@ -1678,7 +1678,7 @@
     "    .CALCULATE(global_avg_balance=AVG(selected_customers.WHERE(account_balance > 0.0).account_balance))\n",
     "    .customers\n",
     "    .CALCULATE(cntry_code=phone[:2])\n",
-    "    .WHERE(is_selected_code & (account_balance > global_avg_balance) & (COUNT(orders) == 0))\n",
+    "    .WHERE(is_selected_code & (account_balance > global_avg_balance) & HASNOT(orders))\n",
     "    .PARTITION(\n",
     "        name=\"countries\",\n",
     "        by=cntry_code,\n",
@@ -1695,7 +1695,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": ".venv",
+   "display_name": "pydough",
    "language": "python",
    "name": "python3"
   },

pydough/conversion/hybrid_syncretizer.py

@@ -224,7 +224,7 @@ def add_extension_semi_anti_count_filter(
             HybridFilter(
                 tree.pipeline[-1],
                 HybridFunctionExpr(
-                    pydop.GRT if is_semi else pydop.EQU,
+                    pydop.NEQ if is_semi else pydop.EQU,
                     [agg_ref, literal_zero],
                     BooleanType(),
                 ),

pydough/conversion/hybrid_tree.py

@@ -324,7 +324,7 @@ def insert_count_filter(self, child_idx: int, is_semi: bool) -> None:
         condition: HybridExpr
         if is_semi:
             condition = HybridFunctionExpr(
-                pydop.GRT,
+                pydop.NEQ,
                 [result_ref, HybridLiteralExpr(Literal(0, NumericType()))],
                 BooleanType(),
             )
@@ -588,6 +588,16 @@ def add_child(
             self
         )
 
+        # Augment the reverse cardinality if the parent does not always exist.
+        if not reverse_cardinality.filters:
+            if len(self.pipeline) == 1 and isinstance(
+                self.pipeline[0], HybridPartition
+            ):
+                if self.parent is not None and not self.parent.always_exists():
+                    reverse_cardinality = reverse_cardinality.add_filter()
+            elif not self.always_exists():
+                reverse_cardinality = reverse_cardinality.add_filter()
+
         # Create and insert the new child connection.
         new_child_idx = len(self.children)
         connection: HybridConnection = HybridConnection(
@@ -601,10 +611,6 @@ def add_child(
         )
         self._children.append(connection)
 
-        # Augment the reverse cardinality if the parent does not always exist.
-        if (not reverse_cardinality.filters) and (not self.always_exists()):
-            connection.reverse_cardinality = reverse_cardinality.add_filter()
-
         # If an operation prevents the child's presence from directly
         # filtering the current level, update its connection type to be either
         # SINGULAR or AGGREGATION, then insert a similar COUNT(*)/PRESENT
@@ -852,7 +858,7 @@ def is_singular(self) -> bool:
             case _:
                 return False
         # The current level is fine, so check any levels above it next.
-        return True if self.parent is None else self.parent.always_exists()
+        return True if self.parent is None else self.parent.is_singular()
 
     def equals_ignoring_successors(self, other: "HybridTree") -> bool:
         """