Add table alias to SQLTableCheckOperator query

Without a table alias, the query does not run on Postgres and
other databases. The alias is arbitrary and used only for
proper query execution.

airflow/providers/common/sql/operators/sql.py

@@ -269,7 +269,7 @@ class SQLTableCheckOperator(BaseSQLOperator):
 
     sql_check_template = """
         SELECT '_check_name' AS check_name, MIN(_check_name) AS check_result
-        FROM(SELECT CASE WHEN check_statement THEN 1 ELSE 0 END AS _check_name FROM table)
+        FROM(SELECT CASE WHEN check_statement THEN 1 ELSE 0 END AS _check_name FROM table) AS check_table
     """
 
     def __init__(