MySQL 内置数学函数

MySQL 内置数学函数

学习学习mysql内置数学函数，先进入mysql：

C:\Users\Administrator>cd /d D:\MySQL Server 5.5\binD:\MySQL Server 5.5\bin>mysql -u root -pEnter password: ********Welcome to the MySQL monitor. Commands end with ; or \g.Your MySQL connection id is 1Server version: 5.5.28 MySQL Community Server (GPL)Copyright (c) 2000, 2012, Oracle and/or its affiliates. All rights reserved.Oracle is a registered trademark of Oracle Corporation and/or itsaffiliates. Other names may be trademarks of their respectiveowners.Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.mysql>

如直接输入以下命令，却出现：

说明没有设置系统的环境变量。

我们需要把Mysql bin文件夹的地址添加到windows的“环境变量”/“系统变量”/path 中

如出现

ERROR 2003 (HY000): Can't connect to MySQL server on 'localhost' (10061)的错误，应该是mysql服务没有开启。以管理员身份运行cmd，开启即可。还不懂就看：

数学函数：

abs(x) 返回数字的绝对值

floor(x) 返回不大于x的最大整数

rand() 返回0至1的随机数

rand(x) 也返回随机数，不过x作为种子

值

mysql> select abs(-2),floor(1.5),rand(),rand(),PI();+---------+------------+--------------------+--------------------+----------+| abs(-2) | floor(1.5) | rand() | rand() | PI() |+---------+------------+--------------------+--------------------+----------+| 2 | 1 | 0.8543179415672253 | 0.6597909654116174 | 3.141593 |+---------+------------+--------------------+--------------------+----------+

TRUNCAT用于单纯的截取小数。

mysql> select TRUNCATE(5.242354,4);+----------------------+| TRUNCATE(5.242354,4) |+----------------------+| 5.2423 |+----------------------+

round()四舍五入取最近整数。

round(x,y)保留x小数点后y位的值

mysql> select round(5.242354,4);+-------------------+| round(5.242354,4) |+-------------------+| 5.2424 |+-------------------+mysql> select round(1.4),round(1.5),round(1.6);+------------+------------+------------+| round(1.4) | round(1.5) | round(1.6) |+------------+------------+------------+| 1 | 2 | 2 |+------------+------------+------------+

sign(x) 判断x的正负性。 x>0: 1  x<0: -1 x=0: 0

mysql> select sign(4),sign(-4),sign(0);+---------+----------+---------+| sign(4) | sign(-4) | sign(0) |+---------+----------+---------+| 1 | -1 | 0 |+---------+----------+---------+

pow(x,y)

sqrt(x)

EXP(x) 返回e的x乘方后的值

mod(x,y)  返回 x mod y的值

log(x) 返回

的值

log10(x)

mysql> select pow(2,6),sqrt(64),exp(2),mod(65,64),log(64),log10(100);+----------+----------+------------------+------------+--------------------+------------+| pow(2,6) | sqrt(64) | exp(2) | mod(65,64) | log(64) | log10(100) |+----------+----------+------------------+------------+--------------------+------------+| 64 | 8 | 7.38905609893065 | 1 | 4.1588830833596715 | 2 |+----------+----------+------------------+------------+--------------------+------------+

和角度相关的函数：

radians(x) 角度转弧度

degrees(x) 弧度转角度

mysql> select radians(180),degrees(PI());+-------------------+---------------+| radians(180) | degrees(PI()) |+-------------------+---------------+| 3.141592653589793 | 180 |+-------------------+---------------+

三角函数相关的函数：

mysql> select sin(PI()/2),cos(PI()/2.0),acos(0),tan(PI()/4.0),atan(1);+-------------+-----------------------+--------------------+--------------------+--------------------+| sin(PI()/2) | cos(PI()/2.0) | acos(0) | tan(PI()/4.0) | atan(1) |+-------------+-----------------------+--------------------+--------------------+--------------------+| 1 | 6.123233995736766e-17 | 1.5707963267948966 | 0.9999999999999999 | 0.7853981633974483 |+-------------+-----------------------+--------------------+--------------------+--------------------+

参数都是弧度。

小瑕疵，浮点误差T_T

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