例子：
select * from tb_students where name='jay'
select * from tb_students where name='JAY'
这两句查询结果是一样的
区分大小写需要加入 collate Chinese_PRC_CS_AS：
select * from tb_students where name collate Chinese_PRC_CS_AS='jay'
select * from tb_students where name collate Chinese_PRC_CS_AS='JAY'
CI：不区分大小写，CS：区分大小写。
AI：不区分重音，AS：区分重音。
Omitted：不区分大小写，WS:指定区分大小写。
group by 区分大小写:
select name collate Chinese_PRC_CS_AI) from tb_students
group by name collate Chinese_PRC_CS_AI