在PHP中计算数据库中数据总和和百分比的最佳方法是什么？

Use PHP and MySQL, my table is something like that, 1st field 'id', 2nd field 'score' and etc. I want to get the scores from rows which id<20 and also want sum of scores for all rows and percentages for score in each row. Does it has other way to get sum and percentages from table rather than calculate by PHP statement outside sql statement? Use PHP and MySQL, my table is something like t