Not sure I fully understand the question, but you can create queries in the front end of ePO, then once it is created, put a check-mark next to it, hit Actions > View SQL, then run the query in the back end.
Once you have done that a couple times you can start learning the ePO tables and the joining, then start creating your own. That help?
first of all, i want to say thank you for your reply. Yes, i have already seen the sql query command but it doesnt't seem that i can edit those command. Right now,i have some idea to create new query using sql command but i need to use sql studio to query. Is there anyway on epo to create sql query
You can't edit those SQL commands in the front end (ePO), they are only editable within SSMS (sql server management studio). There is no way within the front end of ePO to edit the actual SQL; this can only be done on the backend via an IDE like SSMS.
However, that does not stop you from going into an IDE and start querying the DB however you like. What I found useful was creating queries in the front end and then viewing the SQL behind them like in my original post. Then you can familiarize yourself with the tables, joining, sprocs, views, etc. and then be able to write queries when needed from the backend.