Mysql常用运算符与函数汇总

我们先把数据表建好

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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' );

常用的运算符:
1: 等于( = )

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1 2	select * from employee where sal = 3800; select * from employee where sal = null ;  --这里查询不到为null的数据

2: 等于( <=> )

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1 2	select * from employee where sal <=> 3800; select * from employee where sal <=> null ; --这里可以查询到为null的数据

3: is判断(null)

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1 2	select * from employee where sal is null ; select * from employee where sal is not null ;

4: null值判断还可以使用isnull();

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1 2	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不为包括进去

7: and 和 or

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1 2	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(>), 小于等于(<=), 大于等于(>=)

    select * from employee where sal >= 4500;

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数学函数
1: rand();

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select rand() from dual; --dual是一个伪表 select 1+1 from dual; select rand(); --可以简写

2: least(value1, value2, ...) 返回最小值

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1 2	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; --列名可以起一个别名

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表示要保留几们小数,默认值是0

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1 2	select round(1.69); select round(1.69, 1);

5: abs() 绝对值

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1 2	select 5-10; select abs (5-10);

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汇总函数

1: avg(); 

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1 2	select * from employee where sal >= 6000; select avg (sal) from employee where sal >= 6000;

2: count()

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select count (*) from employee; select count (emp_name) from employee; select count (sal) from employee;  --打印9 这里会忽略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: 获取当前的日期时间

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select now(), sysdate(), current_timestamp (); select now(6), sysdate(6), current_timestamp (6); ps: now(), current_timestamp ();没有区别, 表示sql开始执行时的时间   sysdate()表示这个函数开始时间

2: 获取当前日期

    select curdate();   --只有年月日

3: 获取当前时间

    select curtime();   --只有时分秒

4: 日期的加运算date_add     

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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: 计算日期差

    select history, sysdate(), datediff(sysdate(), history) from employee;     --以天数来表示

7: 获取日期的指定部分(把日期转换为指定的格式)  date_format()

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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: 计算出一个日期是星期几

    select history, dayname(history) from employee;

9: 中文日期字符串转换日期str_to_date()
 

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1 2	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则表示12小制, 如果是大H则表示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起始位置, 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(替换

    select replace(emp_name, '李', '老') from employee where emp_name = '李四';

原文链接：http://www.cnblogs.com/wadmwz/archive/2017/09/20/7558776.html