using System.Text;
public DataTable Select(string A,string B)
{
StringBuilder sb=new StringBuilder("SELECT * FROM tablename WHERR 1=1");
sb.Append(A==String.Empty? "":"AND Column1='"+A+"'");
sb.Append(B==String.Empty? "":"AND Column2='"+B+"'");
//如果有更多的查询参数,可以继续Append;
string sqlSelect=sb.ToString();
//下面就是返回你按条件查询得的DataTable了
}