hymn

需求：按照指定字符串排序，

分析：运用 FIRLD 可以实现

问题：字段中有null 值，需要放到最后

// 在排序前加 rating is null 并且 在 FLELD 中加 IFNULL(rating,"")
SELECT * 
FROM `dl_school`
ORDER BY rating is null,FIELD(rating,"A+","A","A-",IFNULL(rating,"")),sort DESC