网站弹出窗口js,大学网站开发专业怎么样,建站与备案的具体流程是什么,软件生命周期七个阶段文章目录 1.日期函数2.字符串函数3.数学函数4.其它函数 1.日期函数
MySQL中内置了一下函数#xff1a;
函数名称描述current_date()当前日期current_time()当前时间current_timestamp()当前时间戳date(datetime)返回datetime参数的日期部分date_add(date,interval d_value_t… 文章目录 1.日期函数2.字符串函数3.数学函数4.其它函数 1.日期函数
MySQL中内置了一下函数
函数名称描述current_date()当前日期current_time()当前时间current_timestamp()当前时间戳date(datetime)返回datetime参数的日期部分date_add(date,interval d_value_type)在date中添加日期或时间interval后的数值单位可以是year minute second daydate_sub(date,interval d_value_type)在date中减去日期或时间interval后的数值单位可以是year minute second daydatediff(date1,date2)两个日期的差单位是天now()当前日期时间
获得年月日
mysql select current_date();
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| current_date() |
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| 2023-11-11 |
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1 row in set (0.00 sec)获得时分秒
mysql select current_time();
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| current_time() |
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| 15:46:47 |
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1 row in set (0.00 sec)获得时间戳
mysql select current_timestamp();
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| current_timestamp() |
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| 2023-11-11 15:47:19 |
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1 row in set (0.00 sec)在日期的基础上加日期
mysql select date_add(2023-11-11,interval 10 day);
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| date_add(2023-11-11,interval 10 day) |
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| 2023-11-21 |
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1 row in set (0.01 sec)在日期的基础上减去时间
mysql select date_sub(2023-11-11,interval 10 day);
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| date_sub(2023-11-11,interval 10 day) |
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| 2023-11-01 |
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1 row in set (0.00 sec)计算两个日期之间相差多少天
mysql select datediff(2023-11-11,2023-10-21);
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| datediff(2023-11-11,2023-10-21) |
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| 21 |
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1 row in set (0.01 sec)创建一个留言表
mysql create table messsage(- id int primary key auto_increment,- content varchar(32) not null,- sendtime datetime- );
Query OK, 0 rows affected (0.03 sec)插入数据
mysql insert into message(content,sendtime) values(hello world,now());
mysql insert into message(content,sendtime) values(hello world,now());
mysql select * from message;
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| id | content | sendtime |
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| 3 | hello world | 2023-11-11 16:03:38 |
| 4 | hello world | 2023-11-11 16:03:48 |
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2 rows in set (0.00 sec)请查询在2分钟内发布的帖子
mysql select * from message where date_add(sendtime ,interval 2 minute) now();
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| id | content | sendtime |
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| 3 | hello world | 2023-11-11 16:03:38 |
| 4 | hello world | 2023-11-11 16:03:48 |
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2 rows in set (0.00 sec)------------------------------|-----------|-------------|------------------初始时间 now() 初始时间2min2.字符串函数
函数名称描述charset(str)返回字符串字符集concat(string2 [,…])连接字符串instr(string,substring)返回substring在string中出现的位置没有返回0ucase(string2)转换成大写lcase(string2)转换成小写left(string2,length)从string2中的左边取length个字符right(string2,length)从string2中的右边取length个字符length(string)string的长度replace(str, search_str, replace_str)在str中用replace_str 替换search_strstrcmp(string1, string2)逐字符比较两个字符串大小substring(str, position [,length])从str的postion开始取length个字符ltrim(string) rtrim(string) trim(string)去除前空格或后空格
获取emp表的ename列的字符集
select charset(ename) from emp;要求显示exam_result表中的信息显示格式“XXX的语文是XXX分数学XXX分英语XXX分”
select concat(name, 的语文是,chinese,分数学是,math,分) as 分数 from student;求学生表中学生姓名占用的字节数
select length(name), name from student;注意length函数返回字符串长度以字节为单位。如果是多字节字符则计算多个字节数如果是单字节字符则算作一个字节。比如字母数字算作一个字节中文表示多个字节数与字符集编码有关
将emp表中所有名字中有S的替换成’上海’
select replace(ename, S, 上海) ,ename from emp;截取emp表中ename字段的第二个到第三个字符
select substring(ename, 2, 2), ename from emp;以首字母小写的方式显示所有员工的姓名
select concat(lcase(substring(ename,1,1)),substring(ename,2)) from emp;3.数学函数
函数名称描述abs(number)绝对值bin(decimal_number)十进制转换二进制hex(decimalNumber)转换成十六进制conv(number,from_base,to_base)进制转换ceiling(number)向上取整floor(number)向下取整format(number,decimal_places)格式化保留小数位数rand()返回随机浮点数范围[0.0,1.0)mod(number,denominator)取模求余
绝对值
select abs(-100.2);
mysql select abs(-100.2);
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| abs(-100.2) |
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| 100.2 |
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1 row in set (0.00 sec)向上取整
mysql select ceiling(3.1);
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| ceiling(3.1) |
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| 4 |
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1 row in set (0.00 sec)mysql select ceiling(3.9);
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| ceiling(3.9) |
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| 4 |
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1 row in set (0.00 sec)mysql select ceiling(-3.1);
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| ceiling(-3.1) |
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| -3 |
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1 row in set (0.00 sec)mysql select ceiling(-3.9);
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| ceiling(-3.9) |
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| -3 |
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1 row in set (0.00 sec向下取整
mysql select floor(3.1);
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| floor(3.1) |
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| 3 |
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1 row in set (0.00 sec)mysql select floor(3.9);
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| floor(3.9) |
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| 3 |
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1 row in set (0.00 sec)mysql select floor(-3.1);
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| floor(-3.1) |
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| -4 |
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1 row in set (0.00 sec)mysql select floor(-3.9);
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| floor(-3.9) |
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| -4 |
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1 row in set (0.00 sec)保留2位小数位数小数四舍五入)
mysql select format(12.345,2);
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| format(12.345,2) |
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| 12.35 |
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1 row in set (0.00 sec)mysql select format(99.99,2);
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| format(99.99,2) |
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| 99.99 |
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1 row in set (0.00 sec)mysql select format(99.999,2);
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| format(99.999,2) |
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| 100.00 |
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1 row in set (0.00 sec)
mysql select format(-12.223,2);
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| format(-12.223,2) |
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| -12.22 |
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1 row in set (0.00 sec)mysql select format(-12.227,2);
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| format(-12.227,2) |
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| -12.23 |
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1 row in set (0.00 sec)产生随机数
mysql select rand();
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| rand() |
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| 0.5963675860281732 |
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1 row in set (0.00 sec)mysql select rand()*10;
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| rand()*10 |
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| 3.1565381243420187 |
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1 row in set (0.00 sec)
4.其它函数
user() 查询当前用户
select user();
mysql select user();
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| user() |
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| rootlocalhost |
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1 row in set (0.00 sec)database()显示当前正在使用的数据库
select database();
mysql select database();
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| database() |
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| scott |
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1 row in set (0.00 sec)md5(str)对一个字符串进行md5摘要摘要后得到一个32位字符串
select md5(admin);
mysql select md5(admin);
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| md5(admin) |
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| 21232f297a57a5a743894a0e4a801fc3 |
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1 row in set (0.00 sec)password()函数MySQL数据库使用该函数对用户加密
select password(root);
mysql select password(root);
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| password(root) |
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| *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
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1 row in set, 1 warning (0.01 sec)ifnullval1 val2 如果val1为null返回val2否则返回val1的值
mysql select ifnull(abc,null);
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| ifnull(abc,null) |
--------------------
| abc |
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1 row in set (0.00 sec)mysql select ifnull(null, 123);
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| ifnull(null, 123) |
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| 123 |
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1 row in set (0.00 sec)mysql select ifnull(abc, 123);
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| ifnull(abc, 123) |
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| abc |
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1 row in set (0.00 sec)
