Merge pull request ClickHouse#72304 from ClickHouse/fix_postgres_utility

Fix check in `test_postgresql_replica_database_engine_2`

Author: alexey-milovidov

tests/integration/helpers/postgres_utility.py

@@ -342,12 +342,22 @@ def assert_nested_table_is_created(
         table = schema_name + "." + table_name
 
     print(f"Checking table {table} exists in {materialized_database}")
-    database_tables = instance.query(f"SHOW TABLES FROM `{materialized_database}`")
 
-    while table not in database_tables:
-        time.sleep(0.2)
-        database_tables = instance.query(f"SHOW TABLES FROM `{materialized_database}`")
+    # Check based on `system.tables` is not enough, because tables appear there before they are loaded.
+    # It may lead to error `Unknown table expression identifier...`
+    while True:
+        try:
+            instance.query(
+                f"SELECT * FROM `{materialized_database}`.`{table}` LIMIT 1 FORMAT Null"
+            )
+            break
+        except Exception:
+            time.sleep(0.2)
+            continue
 
+    database_tables = instance.query(
+        f"SHOW TABLES FROM `{materialized_database}` WHERE name = '{table}'"
+    )
     assert table in database_tables