Transfer select result to sql query as variable

I have 3 selectbox and one list grid in the same form. Currently I want to transfer the selected value to list grid to load data that sql query has 3 fliter condition. How could I transfer the field value into sql query without submitted ?(e.g. selected values are A, B, C, and list grid sql query will load data as select ... from table where q1 = A and q2 = B and q3 = C)