Select Statement or Function Module

Hi all,

I have lakhs of records in my database.When I am using the SAP standard function module C1F2_SUBSTANCES_READ for retreiving data it is taking time.I know all the data base tables .Shall I use to retreive data using select statements instead of the mentioned SAP standard function module.Could any one please explain which is best method to retrieve huge data and also explain reason?

Thanks and Regards,

Kanth