表生成函数：可以理解为一个函数可以生成一个表
行转列函数：explode(字段名)----炸开字段内容
distinct去重
select distinct sub from (select explode(subjects) as sub from t_stu_subject) temp;
表生成函数：lateral view
目标表
select id,name,tmp.sub
from t_stu_subject later view wxplode(subjects) tmp as sub;