MySQL数据可的deleteupate语句和常用函数

Posted 2020-10-26

1、删除数据

例如：把所有性别为空的数据删除

mysql> delete from student where Gender is null;

例如：把ID为2,4的数据删除

mysql> delete from student where ID in (2,4);

2、清空数据表，只留表结构

mysql> truncate table student;

3、修改数据

mysql> update student  set Score=80 where Name="肖清华";

4、统计字符串的字节数length()，字符数char_length()

mysql> select * from student where char_length(Name)=3;    //查询Name是三个字的人，也可以使用以下方法

mysql> select * from student where Name like "___";

5、 查询指定时间内的数据    

mysql> create table member(

    ID int unsigned not null auto_increment,

    Account varchar(30) not null unique,

    Pass varchar(32),

    Regtime datetime,

    primary key(ID));               //新创建一个测试表

mysql> insert into member values(null,"李四","123456","2018-03-08");     

mysql> insert into member values(null,"王五","1234567","2018-02-08");

mysql> insert into member values(null,"赵六","1234557","2017-02-08");

mysql> insert into member values(null,"夏明","123457","2017-12-08");         //插入测试数据

要求：统计近五天内注册的会员人数

mysql> select count(*) from member where Regtime between date_add(now(),interval -5 day) and now();

mysql> select * from member where Regtime between date_add(now(),interval -5 day) and now();

6、格式化输出

mysql> select Account 账号,date_format(Regtime,"%Y年%m月%d日") 注册日期 from member;

7、查询当前系统的时间戳，然后转换成年月日格式

mysql> select unix_timestamp() 系统时间戳;

mysql> select from_unixtime(1520494242);

mysql> select date_format(from_unixtime(1520494242),"%Y年%m月%d日");

8、将字符串连接

mysql> select concat("年龄:",Age) from student;

mysql> select concat_ws("-","年龄",Age) from student;   //也是字符的拼接，只不过在字符中间加上了“-”

9、重复输出，比如输出十个"#"

mysql> select repeat("#",10);

mysql> select space(10);  //输出十个空格

10、大小写转换

mysql> select upper(Name) from student where Name like "w%";    //upper把小写字母转换为大写字母

mysql> select lower(Name) from student where Name like "w%";    //lower把大写字母转换为小写字母

11、字符截取

mysql> select left(Name,1) from student;       //left截取左边第一个字符

mysql> select right(Address,3) from student;    //right截取右边的字符

mysql> select mid(Address,2) from student;     //mid从第几个字符开始截取，这里的首字符是1

mysql> select mid(Address,1,3) from student;    //从第几个开始到第几个结束

12、if函数使用

等级：90优秀，70良好，60及格，以下补考

mysql> select Name 姓名,Gender 性别,Score 成绩,if(Score>=90,"优秀",if(Score>=70,"良好",if(Score>=60,"及格","补考"))) 等级 from student;

13、uuid()生成唯一字符串

mysql> select uuid(),length(uuid());   //并查看长度

14、格式化数字

mysql> select format(1000,2);  //将显示1000.00

15、将IP转换为数字

mysql> select inet_aton("192.168.200.101");

16、将数字转换为IP

mysql> select inet_ntoa("3232286821");