-- 查询测试表数据
select * from test
-- 对avg列进行升序
select kechenghao,avg as avg from test ORDER BY avg asc
-- 对avg列升序，然后对课程表进行降序，注意 课程表数字的变化
select kechenghao,avg as avg from test ORDER BY avg asc, kechenghao desc
-- 对课程表单独进行降序
select kechenghao,avg as avg from test ORDER BY kechenghao desc
总结：先升序，再降序：根据语法来理解是：先根据avg进行排序，然后再调整avg对应的课程表顺序
select kechenghao,avg as avg from test ORDER BY avg asc, kechenghao desc