Fix duplicate CTEs in SQL build v2

datajunction-server/datajunction_server/construction/build_v2.py

@@ -1793,10 +1793,15 @@ def convert_to_cte(
     """
     Convert the query to a CTE that can be used by the outer query
     """
-    # Move all the CTEs used by the inner query to the outer query
+    # Move all the CTEs used by the inner query to the outer query,
+    # deduplicating by CTE name to avoid duplicate CTEs
+    existing_cte_names = {cte.alias_or_name.identifier() for cte in outer_query.ctes}
     for cte in inner_query.ctes:
-        cte.set_parent(outer_query, parent_key="ctes")
-    outer_query.ctes.extend(inner_query.ctes)
+        cte_identifier = cte.alias_or_name.identifier()
+        if cte_identifier not in existing_cte_names:  # pragma: no branch
+            cte.set_parent(outer_query, parent_key="ctes")
+            outer_query.ctes.append(cte)
+            existing_cte_names.add(cte_identifier)
     inner_query.ctes = []
 
     # Convert the dimension node query to a CTE
@@ -2136,10 +2141,21 @@ async def build_ast(
     # Apply pushdown filters if possible
     apply_filters_to_node(node, query, to_filter_asts(filters))
 
+    # Add new CTEs while deduplicating by CTE name
+    existing_cte_names = {cte.alias_or_name.identifier() for cte in query.ctes}
     for cte in new_cte_mapping.values():
-        query.ctes.extend(cte.ctes)
+        # Add nested CTEs from this CTE, deduplicating
+        for nested_cte in cte.ctes:  # pragma: no branch
+            nested_cte_id = nested_cte.alias_or_name.identifier()
+            if nested_cte_id not in existing_cte_names:  # pragma: no branch
+                query.ctes.append(nested_cte)
+                existing_cte_names.add(nested_cte_id)
         cte.ctes = []
-        query.ctes.append(cte)
+        # Add the CTE itself if not already present
+        cte_id = cte.alias_or_name.identifier()
+        if cte_id not in existing_cte_names:  # pragma: no branch
+            query.ctes.append(cte)
+            existing_cte_names.add(cte_id)
     query.select.add_aliases_to_unnamed_columns()
     ctes_mapping.update(new_cte_mapping)
     return query