Add a column to the data queried in the SQL statement, and add a default value

Query out data, and add data that is not present in the list, and the values of this column are equal

Select App_id,app_secret from Wx_ticket Group by app_id;

The data that is queried is

app_id | Expires_in
--------------------+------------
WXEEC89CDF2D435D10 | 7200
WXEEC89CDF2D435D10 | 7200
wx9b7bfb5f59df5009 | 7200
wx9b7bfb5f59df5009 | 7200
wx649ae9eecb72227d | 7200
wx649ae9eecb72227d | 7200

When using select ' 20150429 ' Date,app_id,app_secret from Wx_ticket Group by app_id;

Date | app_id | Expires_in
----------+--------------------+------------
20150429 | WXEEC89CDF2D435D10 | 7200
20150429 | WXEEC89CDF2D435D10 | 7200
20150429 | wx9b7bfb5f59df5009 | 7200
20150429 | wx9b7bfb5f59df5009 | 7200
20150429 | wx649ae9eecb72227d | 7200
20150429 | wx649ae9eecb72227d | 7200
20150429 | WXC01E853C2A2745C9 | 7200
20150429 | wx911d98d37516611c | 7200

Add a column to the data queried in the SQL statement, and add a default value