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绝对值函数ABS(x)和圆周率函数PI()
mysql> SELECT ABS(0.5), ABS(-0.5), PI();+----------+-----------+----------+| ABS(0.5) | ABS(-0.5) | PI() |+----------+-----------+----------+| 0.5 | 0.5 | 3.141593 |+----------+-----------+----------+1 row in set (0.00 sec)
平方根函数SQRT(x)和求余函数MOD(x,y)
mysql> SELECT SQRT(16), SQRT(3), MOD(13,4);+----------+--------------------+-----------+| SQRT(16) | SQRT(3) | MOD(13,4) |+----------+--------------------+-----------+| 4 | 1.7320508075688772 | 1 |+----------+--------------------+-----------+1 row in set (0.00 sec)
取整函数CEIL(x)、CEILING(x)和FLOOR(x)
mysql> SELECT CEIL(2.3), CEIL(-2.3), CEILING(2.3), CEILING(-2.3);+-----------+------------+--------------+---------------+| CEIL(2.3) | CEIL(-2.3) | CEILING(2.3) | CEILING(-2.3) |+-----------+------------+--------------+---------------+| 3 | -2 | 3 | -2 |+-----------+------------+--------------+---------------+1 row in set (0.00 sec)mysql> SELECT FLOOR(2.3), FLOOR(-2.3);+------------+-------------+| FLOOR(2.3) | FLOOR(-2.3) |+------------+-------------+| 2 | -3 |+------------+-------------+1 row in set (0.00 sec)
CEIL(x)和CEILING(x)返回大于或等于x的最小整数
FLOOR(x)返回小于或等于x的最大整数
随机数函数RAND()和RAND(x)
mysql> SELECT RAND(), RAND(2), RAND(2);+--------------------+--------------------+--------------------+| RAND() | RAND(2) | RAND(2) |+--------------------+--------------------+--------------------+| 0.8269294489425881 | 0.6555866465490187 | 0.6555866465490187 |+--------------------+--------------------+--------------------+1 row in set (0.00 sec)
RAND()和RAND(x)这两个函数丢失返回0～1的随机数
区别在于，RAND()返回的数是完全随机的，而RAND(x)在x相同时返回的值相同
四舍五入函数ROUND(x)、ROUND(x,y)和TRUNCATE(x,y)
mysql> SELECT ROUND(2.3), ROUND(2.5), ROUND(2.53,1), ROUND(2.55,1);+------------+------------+---------------+---------------+| ROUND(2.3) | ROUND(2.5) | ROUND(2.53,1) | ROUND(2.55,1) |+------------+------------+---------------+---------------+| 2 | 3 | 2.5 | 2.6 |+------------+------------+---------------+---------------+1 row in set (0.00 sec)
ROUND(x)返回离x最近的整数，也就是对x进行四舍五入处理
PHP高级开发技巧与范例
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PHP是一种功能强大的网络程序设计语言，而且易学易用，移植性和可扩展性也都非常优秀，本书将为读者详细介绍PHP编程。 全书分为预备篇、开始篇和加速篇三大部分，共9章。预备篇主要介绍一些学习PHP语言的预备知识以及PHP运行平台的架设；开始篇则较为详细地向读者介绍PKP语言的基本语法和常用函数，以及用PHP如何对MySQL数据库进行操作；加速篇则通过对典型实例的介绍来使读者全面掌握PHP。 本书
ROUND(x,y)返回x保留到小数点后y位的值，在截取时进行四舍五入处理
mysql> SELECT TRUNCATE(2.53,1), TRUNCATE(2.55,1);+------------------+------------------+| TRUNCATE(2.53,1) | TRUNCATE(2.55,1) |+------------------+------------------+| 2.5 | 2.5 |+------------------+------------------+1 row in set (0.00 sec)
TRUNCATE(x,y)返回x保留到小数点后y位的值，不进行四舍五入操作
符号函数SIGN(x)
mysql> SELECT SIGN(-2), SIGN(0), SIGN(2);+----------+---------+---------+| SIGN(-2) | SIGN(0) | SIGN(2) |+----------+---------+---------+| -1 | 0 | 1 |+----------+---------+---------+1 row in set (0.00 sec)
SIGN(x)返回x的符号，-1为负数，0不变，1为整数
幂运算函数POW(x,y)、POWER(x,y)
mysql> SELECT POW(3,2), POWER(3,2);+----------+------------+| POW(3,2) | POWER(3,2) |+----------+------------+| 9 | 9 |+----------+------------+1 row in set (0.00 sec)
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