Now there is a table, there are about more than 50 ten thousand records, you need to set some of these records placed at the top, if add a field isTop alone, isTop numerical value, the greater the order the more, can achieve, but if you don't add index, efficiency is very low, if add index, because most of the record is not placed at the top (isTop 0), such sort, efficiency is not good, is there a better realization method of the great god, please give directions, thank you