sql复杂排序

在很多人都知道排序用ORDER BY  但是在复杂的排序的时候，就会发现 ORDER BY这个关键字怎么排序也满足不了需求了。 这时候就要说今天关键字了UNION ALL 了 ，很多人就不理解了，这不是对两个结果集进行并集，

排序规则：优先展示

1.age<18

2. sex =0

3.按照名字排序

( SELECT i.*,1 AS sort FROM info AS i WHERE age < 18 AND sex = 0   ORDER BY convert('name' using gbk) asc LIMIT 999999) 
UNION ALL
(SELECT	 i.*,2 AS sort FROM info AS i WHERE age < 18  AND sex = 1  ORDER BY convert('name' using gbk) asc LIMIT 999999)
UNION ALL
(SELECT	 i.*,3 AS sort FROM info AS i WHERE age > 18  AND sex = 0  ORDER BY convert('name' using gbk) asc LIMIT 999999)
UNION ALL
(SELECT	 i.*,4 AS sort FROM info AS i WHERE age > 18  AND sex = 1  ORDER BY convert('name' using gbk) asc LIMIT 999999)