add some usage at README.md.

Author: sn0wfree

ClickSQL/clickhouse/ClickHouse.py

@@ -114,7 +114,7 @@ def __init__(self, **db_settings):
         self._test_connection_()
 
     @staticmethod
-    def _check_db_settings(db_settings: dict, available_db_type=[node.__name__]): # node.__name__ : clickhouse
+    def _check_db_settings(db_settings: dict, available_db_type=[node.__name__]):  # node.__name__ : clickhouse
         """
         it is to check db setting whether is correct!
         :param db_settings:

ClickSQL/clickhouse/ClickHouseExt.py

@@ -191,7 +191,7 @@ def _create_table_from_df(cls, db: str, table: str, df: pd.DataFrame, key_cols:
         dtypes_dict = {k: v for k, v in dtypes_dict.items() if k in cols}
         base = cls._create_table_from_sql(db, table, dtypes_dict, key_cols, engine_type=engine_type,
                                           extra_format_dict=extra_format_dict, partitions_expr=partitions_expr)
-        # exist_status = cls._check_table_exists(obj, db, table)
+        exist_status = cls._check_table_exists(obj, db, table)
 
         query_func(base)
         return exist_status

README.md

@@ -18,17 +18,52 @@ more information for ClickHouse can be found at [here](http://clickhouse.tech)
 `pip install ClickSQL`
 
 ## Usage
+### initial connection
 
+#### *Approach 1*
 ```python
 from ClickSQL import ClickHouseTableNode
 
 conn_str = "clickhouse://default:test121231@99.99.9.9:8123/system"
-ClickHouseTableNode(conn_str)
+ct = ClickHouseTableNode(conn_str)
 
 >>> connection test:  Ok.
 
 ``` 
 
+#### *Approach 2*
+```python
+from ClickSQL import ClickHouseTableNode
+
+
+
+conn_str = {'name':'clickhouse','host':'99.99.9.9','port':8123,'user':'default',
+            'password':'test121231','database':'system'}
+ct = ClickHouseTableNode(conn_str)
+
+>>> connection test:  Ok.
+
+``` 
+### Query
+
+```python
+from ClickSQL import ClickHouseTableNode
+
+conn_str = "clickhouse://default:test121231@99.99.9.9:8123/system"
+ct = ClickHouseTableNode(conn_str)
+
+ct.query('show tables from system limit 1')
+
+>>> connection test:  Ok.
+>>>                             name
+>>> 0  aggregate_function_combinators
+```
+
+### Contribution
+there is welcome to do more work to improve this package more convenient
+
+## Author
+sn0wfree