我们先来看个示例
use test; create table `employee`( emp_no int unsigned, emp_name varchar(30), emp_sex varchar(3), emp_age tinyint unsigned, sal double, history datetime ); insert into employee values(1, '张三', '男', 18, 5000, '2012-04-23'), (2, '李四', '男', 27, 4500, '2013-05-23'), (3, '王五', '男', 23, 4700, '2012-04-21'), (4, '子龙', '男', 19, 3800, '2011-03-04'), (5, '李白', '男', 15, 6200, '2015-09-09'), (6, '刘备', '男', 28, 2500, '2016-02-11'), (7, '吕布', '男', 21, 6000, '2010-10-18'), (8, '尚香', '女', 16, 4500, '2011-09-26'), (9, '小乔', '女', 15, null, '2013-07-05'), (10, '大乔', '女', 16, 5000, '2017-09-01');
经常运用的运算符:
1: 即是( = )
select * from employee where sal = 3800; select * from employee where sal = null; --这里查询不到为null的数据
2: 即是( <=> )
select * from employee where sal <=> 3800; select * from employee where sal <=> null; --这里能够查询到为null的数据
3: is推断(null)
select * from employee where sal is null; select * from employee where sal is not null;
4: null值推断还能够运用isnull();
select * from employee where isnull(sal); select * from employee where !isnull(sal);
5: 在区间(between)内 between min and max ps:这里是一个闭区间
select * from employee where sal between 4500 and 5000;
6: 不在区间内
select * from employee where sal not between 4500 and 5000; --null不为包含进去
7: and 和 or
select * from employee where sal not between 4500 and 5000 or sal is null; select * from employee where sal = 4500 and emp_sex = '女';
8: 小于(<), 大于(>), 小于即是(<=), 大于即是(>=)
select * from employee where sal >= 4500;
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数学函数
1: rand();
select rand() from dual; --dual是一个伪表 select 1+1 from dual; select rand(); --能够简写
2: least(value1, value2, ...) 返回最小值
select least(54,76,4,65,76,87,87,56,65,654,45,23,1,76); select least(54,76,4,65,76,87,87,56,65,654,45,23,1,76) as min_value; --列名能够起一个别号
3: greatest(value1, value2, ...) 返回最大值
select greatest(54,76,4,65,76,87,87,56,65,654,45,23,1,76);
4: round(M, D); 返回M的四舍五入的值, D示意要保存几们小数,默认值是0
select round(1.69); select round(1.69, 1);
5: abs() 绝对值
select 5-10; select abs(5-10);
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汇总函数
1: avg();
select * from employee where sal >= 6000; select avg(sal) from employee where sal >= 6000;
2: count()
select count(*) from employee; select count(emp_name) from employee; select count(sal) from employee; --打印9 这里会疏忽null值 select count(*) from employee where sal >= 4000; select count(*) from employee where sal <= 4000 or sal is null;
3: sum()
select sum(sal) from employee where sal >= 6000;
4: min()
select min(sal) from employee;
5: max()
select max(sal) from employee;
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日期函数
1: 猎取当前的日期时候
select now(), sysdate(), current_timestamp();
select now(6), sysdate(6), current_timestamp(6);
ps: now(), current_timestamp();没有区分, 示意sql最先执行时的时候
sysdate()示意这个函数最先时候
2: 猎取当前日期
select curdate(); --只要年月日
3: 猎取当前时候
select curtime(); --只要时分秒
4: 日期的加运算date_add
select history, date_add(history, interval '1 12:10' day_minute) from employee; --date_add(history, interval '1 12:10' day_minute) select history, date_add(history, interval '1-1' year_month) from employee; --date_add(history, interval '1-1' year_month) select history, date_add(history, interval '1' second) from employee; --date_add(history, interval '1' second)
5: 日期的减运算data_sub
select history, date_sub(history, interval '1-1' year_month) from employee;
6: 盘算日期差
select history, sysdate(), datediff(sysdate(), history) from employee; --以天数来示意
7: 猎取日期的指定部份(把日期转换为指定的花样) date_format()
select history, date_format(history, '%Y年%m月%d号') from employee; select history, date_format(history, '%d号') from employee; select history, date_format(history, '%Y年%m月%d号 %H时%i分%s秒') from employee;
8: 盘算出一个日期是礼拜几
select history, dayname(history) from employee;
9: 中文日期字符串转换日期str_to_date()
insert into employee values(11, '张飞', '男', 22, 3000, '2017年02月01号'); --报错
insert into employee values(11, '张飞', '男', 22, 3000, str_to_date('2017年02月01号', '%Y年%m月%d号 %H时%i分%s秒'));
insert into employee values(12, '二哥', '男', 22, 3000, str_to_date('2017年02月01号 23时02分02秒', '%Y年%m月%d号 %H时%i分%s秒'));
insert into employee values(12, '二哥', '男', 22, 3000, str_to_date('2017年02月01号 11时02分02秒', '%Y年%m月%d号 %h时%i分%s秒'));
ps: 如果是h则示意12小制, 如果是大H则示意24小明制;
字符串函数
1: left(str, len) 返回字符串str的左端len个字符
select left('abcdefg', 5);
2: length()
select length('abcdefg');
3: lower(str) 返回小写的字符串str
select lower('HELLO');
4: substring() 取子字符串, 第二个参数是截取的肇端位置, 第三个参数是要截取的长度
select substring('helloworld',2,3);
5: concat() 字符串拼接
select concat(emp_name, '员工') from employee;
6: replace(替代
select replace(emp_name, '李', '老') from employee where emp_name = '李四';
以上就是Mysql之运算符与函数的总结的细致内容，更多请关注ki4网别的相干文章！
