Mysql常用運算符與函數匯總

2024-07-24 13:14:29

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我們先把數據表建好

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, '張三', '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, '子龍', '男', 19, 3800, '2011-03-04'),(5, '李白', '男', 15, 6200, '2015-09-09'),(6, '劉備', '男', 28, 2500, '2016-02-11'),(7, '呂布', '男', 21, 6000, '2010-10-18'),(8, '尚香', '女', 16, 4500, '2011-09-26'),(9, '小喬', '女', 15, null, '2013-07-05'),(10, '大喬', '女', 16, 5000, '2017-09-01');

常用的運算符:
1: 等于( = )

 select * from employee where sal = 3800; select * from employee where sal = null;  --這里查詢不到為null的數據

2: 等于( <=> )

 select * from employee where sal <=> 3800; select * from employee where sal <=> null; --這里可以查詢到為null的數據

3: is判斷(null)

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

4: null值判斷還可以使用isnull();

 select * from employee where isnull(sal); select * from employee where !isnull(sal);

5: 在區間(between)內 between min and max ps:這里是一個閉區間

select * from employee where sal between 4500 and 5000;

6: 不在區間內

select * from employee where sal not between 4500 and 5000; --null不為包括進去

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(>), 小于等于(<=), 大于等于(>=)

select * from employee where sal >= 4500;

***************************************************************************************************************

數學函數
1: rand();

 select rand() from dual; --dual是一個偽表 select 1+1 from dual; select rand(); --可以簡寫

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; --列名可以起一個別名

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表示要保留幾們小數,默認值是0

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

5: abs() 絕對值

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

***************************************************************************************************************

匯總函數

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 這里會忽略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;

***************************************************************************************************************

日期函數

1: 獲取當前的日期時間

 select now(), sysdate(), current_timestamp(); select now(6), sysdate(6), current_timestamp(6); ps: now(), current_timestamp();沒有區別, 表示sql開始執行時的時間  sysdate()表示這個函數開始時間

2: 獲取當前日期

select curdate(); --只有年月日

3: 獲取當前時間

select curtime(); --只有時分秒

4: 日期的加運算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: 日期的減運算data_sub

select history, date_sub(history, interval '1-1' year_month) from employee;

6: 計算日期差

select history, sysdate(), datediff(sysdate(), history) from employee; --以天數來表示

7: 獲取日期的指定部分(把日期轉換為指定的格式) date_format()

 select history, date_format(history, '%Y年%m月%d號') from employee; select history, date_format(history, '%d號') from employee; select history, date_format(history, '%Y年%m月%d號 %H時%i分%s秒') from employee;

8: 計算出一個日期是星期幾

select history, dayname(history) from employee;

9: 中文日期字符串轉換日期str_to_date()

 insert into employee values(11, '張飛', '男', 22, 3000, '2017年02月01號'); --報錯 insert into employee values(11, '張飛', '男', 22, 3000, str_to_date('2017年02月01號', '%Y年%m月%d號 %H時%i分%s秒'));

    insert into employee values(12, '二哥', '男', 22, 3000, str_to_date('2017年02月01號 23時02分02秒', '%Y年%m月%d號 %H時%i分%s秒'));
    insert into employee values(12, '二哥', '男', 22, 3000, str_to_date('2017年02月01號 11時02分02秒', '%Y年%m月%d號 %h時%i分%s秒'));
    ps: 如果是h則表示12小制, 如果是大H則表示24小明制;

字符串函數

1: left(str, len) 返回字符串str的左端len個字符

select left('abcdefg', 5);

2: length()

select length('abcdefg');

3: lower(str) 返回小寫的字符串str

select lower('HELLO');

4: substring() 取子字符串, 第二個參數是截取的起始位置, 第三個參數是要截取的長度

select substring('helloworld',2,3);

5: concat() 字符串拼接

select concat(emp_name, '員工') from employee;

6: replace(替換