Fixed bug with no parameter prepared statements (#20243)

* Added bug fix

* Pulled out the section needed to be tested

* Added tests

* Passing tests

* Added changelog

* Formatting

---------

Co-authored-by: aldrick.castro <aldrick.castro@d>

Author: aldrickdev

postgres/changelog.d/20243.fixed

@@ -0,0 +1 @@
+Fixed bug where we fail to explain parameterized queries that have no parameters 

postgres/datadog_checks/postgres/explain_parameterized_queries.py

@@ -22,7 +22,7 @@
 SELECT CARDINALITY(parameter_types) FROM pg_prepared_statements WHERE name = 'dd_{query_signature}'
 '''
 
-EXECUTE_PREPARED_STATEMENT_QUERY = 'EXECUTE dd_{prepared_statement}({generic_values})'
+EXECUTE_PREPARED_STATEMENT_QUERY = 'EXECUTE dd_{prepared_statement}{parameters}'
 
 EXPLAIN_QUERY = 'SELECT {explain_function}($stmt${statement}$stmt$)'
 
@@ -143,20 +143,26 @@ def _get_number_of_parameters_for_prepared_statement(self, dbname, query_signatu
         )
         return rows[0][0] if rows else 0
 
+    @tracked_method(agent_check_getter=agent_check_getter)
+    def _generate_prepared_statement_query(self, dbname: str, query_signature: str) -> str:
+        parameters = ""
+        num_params = self._get_number_of_parameters_for_prepared_statement(dbname, query_signature)
+
+        if num_params > 0:
+            null_parameters = ','.join('null' for _ in range(num_params))
+            parameters = f"({null_parameters})"
+
+        return EXECUTE_PREPARED_STATEMENT_QUERY.format(prepared_statement=query_signature, parameters=parameters)
+
     @tracked_method(agent_check_getter=agent_check_getter)
     def _explain_prepared_statement(self, dbname, statement, obfuscated_statement, query_signature):
-        null_parameter = ','.join(
-            'null' for _ in range(self._get_number_of_parameters_for_prepared_statement(dbname, query_signature))
-        )
-        execute_prepared_statement_query = EXECUTE_PREPARED_STATEMENT_QUERY.format(
-            prepared_statement=query_signature, generic_values=null_parameter
-        )
+        prepared_statement_query = self._generate_prepared_statement_query(dbname, query_signature)
         try:
             return self._execute_query_and_fetch_rows(
                 dbname,
                 EXPLAIN_QUERY.format(
                     explain_function=self._explain_function,
-                    statement=execute_prepared_statement_query,
+                    statement=prepared_statement_query,
                 ),
             )
         except Exception as e:

postgres/tests/test_explain_parameterized_queries.py

@@ -191,6 +191,52 @@ def test_explain_parameterized_queries_explain_prepared_statement_no_plan_return
         assert err is None
 
 
+@pytest.mark.unit
+def test_generate_prepared_statement_query_no_parameters(integration_check, dbm_instance):
+    check = integration_check(dbm_instance)
+    check._connect()
+    test_query_signature = "12345678"
+
+    check.check(dbm_instance)
+    if check.version < V12:
+        return
+
+    with mock.patch(
+        'datadog_checks.postgres.explain_parameterized_queries.ExplainParameterizedQueries._get_number_of_parameters_for_prepared_statement',
+        return_value=0,
+    ):
+
+        prepared_statement_query = (
+            check.statement_samples._explain_parameterized_queries._generate_prepared_statement_query(
+                DB_NAME, test_query_signature
+            )
+        )
+        assert prepared_statement_query == f"EXECUTE dd_{test_query_signature}"
+
+
+@pytest.mark.unit
+def test_generate_prepared_statement_query_three_parameters(integration_check, dbm_instance):
+    check = integration_check(dbm_instance)
+    check._connect()
+    test_query_signature = "12345678"
+
+    check.check(dbm_instance)
+    if check.version < V12:
+        return
+
+    with mock.patch(
+        'datadog_checks.postgres.explain_parameterized_queries.ExplainParameterizedQueries._get_number_of_parameters_for_prepared_statement',
+        return_value=3,
+    ):
+
+        prepared_statement_query = (
+            check.statement_samples._explain_parameterized_queries._generate_prepared_statement_query(
+                DB_NAME, test_query_signature
+            )
+        )
+        assert prepared_statement_query == f"EXECUTE dd_{test_query_signature}(null,null,null)"
+
+
 @pytest.mark.integration
 def test_create_prepared_statement_exception(integration_check, dbm_instance):
     check = integration_check(dbm_instance)