MySQL 查询之 limit，distinct，order by 以及字表操作

MySQL 查询之 limit，distinct，order by 以及字表操作

追加字段 ：alter table stu add birthday date;

更新字段： update stu set birthday=('1989/05/05');

                   update stu set birthday=('1990/04/05') where id=4;

排序并限制取出个数：select * from stu  order by id desc limit 4;   递增是asc

                 查找年龄最大的学生：select sname,birthday from stu order by birthday asc limit 1;

                 查找年龄第二大学生：select sname,birthday from stu order by birthday asc limit 1, 1;

                                                   limit No1,No2  从第No1个行开始，取No2个结果。

                 查找比年龄第二大于等于的学生

                                                 select sname,birthday from stu where birthday<=(select birthday
 from stu order by birthday asc limit 1,1);

                  查找学生出生年份：select year(birthday)  from stu;  注意因为birthday是date，所以可以这么做

                         去重                 select distinct year(birthday) as '出生年份'  from stu  ；注意distinct 位置