feat: optimize export_graph for polardb (#1337)

* feat:optimize export_graph

* feat:optimize export_graph

Author: wustzdy

src/memos/graph_dbs/polardb.py

@@ -1800,7 +1800,6 @@ def search_by_fulltext(
             FROM "{self.db_name}_graph"."Memory" m
             CROSS JOIN q
             {where_clause_cte}
-            ORDER BY rank DESC
             LIMIT {top_k};
         """
         params = [tsquery_string]
@@ -2411,56 +2410,47 @@ def _extract_special_filter_values(filter_obj):
         order_clause = """
             ORDER BY ag_catalog.agtype_access_operator(properties, '"created_at"'::agtype) DESC NULLS LAST,id DESC
         """
+        count_query = f"""
+            SELECT COUNT(*) AS total_count
+            FROM "{self.db_name}_graph"."Memory"
+            {where_clause}
+        """
         if include_embedding:
-            node_query = f"""
-                WITH filtered AS (
-                    SELECT id, properties, embedding
-                    FROM "{self.db_name}_graph"."Memory"
-                    {where_clause}
-                )
-                SELECT p.id, p.properties, p.embedding, c.total_count
-                FROM (SELECT COUNT(*) AS total_count FROM filtered) c
-                LEFT JOIN LATERAL (
-                    SELECT id, properties, embedding
-                    FROM filtered
-                    {order_clause}
-                    {pagination_clause}
-                ) p ON TRUE
+            data_query = f"""
+                SELECT id, properties, embedding
+                FROM "{self.db_name}_graph"."Memory"
+                {where_clause}
+                {order_clause}
+                {pagination_clause}
             """
         else:
-            node_query = f"""
-                WITH filtered AS (
-                    SELECT id, properties
-                    FROM "{self.db_name}_graph"."Memory"
-                    {where_clause}
-                )
-                SELECT p.id, p.properties, c.total_count
-                FROM (SELECT COUNT(*) AS total_count FROM filtered) c
-                LEFT JOIN LATERAL (
-                    SELECT id, properties
-                    FROM filtered
-                    {order_clause}
-                    {pagination_clause}
-                ) p ON TRUE
+            data_query = f"""
+                SELECT id, properties
+                FROM "{self.db_name}_graph"."Memory"
+                {where_clause}
+                {order_clause}
+                {pagination_clause}
             """
-        logger.info(f"[export_graph nodes] Query: {node_query}")
+        logger.info(f"[export_graph nodes] count_query: {count_query}")
+        logger.info(f"[export_graph nodes] data_query: {data_query}")
 
         try:
             with self._get_connection() as conn, conn.cursor() as cursor:
-                cursor.execute(node_query)
+                cursor.execute(count_query)
+                count_row = cursor.fetchone()
+                total_nodes = int(count_row[0]) if count_row and count_row[0] is not None else 0
+
+                cursor.execute(data_query)
                 node_results = cursor.fetchall()
             nodes = []
 
             for row in node_results:
                 if include_embedding:
-                    row_id, properties_json, embedding_json, row_total_count = row
+                    row_id, properties_json, embedding_json = row
                 else:
-                    row_id, properties_json, row_total_count = row
+                    row_id, properties_json = row
                     embedding_json = None
 
-                if row_total_count is not None:
-                    total_nodes = int(row_total_count)
-
                 if row_id is None:
                     continue