How to use combined query when no of field are uncertain?

Here is idea i have 6 different fields to allow search if i give the option for user to enter value in any of 6 option or enter combined fields how to use sql query to retrieve the value.  For example the fields are author, publication, price, subject, edition, bookid and if user enter only one value i could search but if user enter more than one if i try combinations then there are many combination. Please suggest me how to define the query?Here i ...