绝对值函数ABS(x)和圆周率函数PI()   复制代码 代码如下:     mysql> SELECT ABS(0.5), ABS(-0.5), PI(); +----------+-----------+----------+ | ABS(0.5) | ABS(-0.5) | PI() | +----------+-----------+----------+ | 0.5 | 0.5 | 3.141593 | +----------+-----------+----------+ row in set (0.00 sec)   平方根函数SQRT(x)和求余函数MOD(x,y)   复制代码 代码如下:     mysql> SELECT SQRT(16), SQRT(3), MOD(13,4); +----------+--------------------+-----------+ | SQRT(16) | SQRT(3) | MOD(13,4) | +----------+--------------------+-----------+ | 4 | 1.7320508075688772 | 1 | +----------+--------------------+-----------+ row in set (0.00 sec)   取整函数CEIL(x)、CEILING(x)和FLOOR(x)   复制代码 代码如下:     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 | +-----------+------------+--------------+---------------+ row in set (0.00 sec)   mysql> SELECT FLOOR(2.3), FLOOR(-2.3); +------------+-------------+ | FLOOR(2.3) | FLOOR(-2.3) | +------------+-------------+ | 2 | -3 | +------------+-------------+ 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)   复制代码 代码如下:     mysql> SELECT RAND(), RAND(2), RAND(2); +--------------------+--------------------+--------------------+ | RAND() | RAND(2) | RAND(2) | +--------------------+--------------------+--------------------+ | 0.8269294489425881 | 0.6555866465490187 | 0.6555866465490187 | +--------------------+--------------------+--------------------+ 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)   复制代码 代码如下:     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 | +------------+------------+---------------+---------------+ 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 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   复制代码 代码如下:     mysql> SELECT TRUNCATE(2.53,1), TRUNCATE(2.55,1); +------------------+------------------+ | TRUNCATE(2.53,1) | TRUNCATE(2.55,1) | +------------------+------------------+ | 2.5 | 2.5 | +------------------+------------------+ 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)   复制代码 代码如下:     mysql> SELECT SIGN(-2), SIGN(0), SIGN(2); +----------+---------+---------+ | SIGN(-2) | SIGN(0) | SIGN(2) | +----------+---------+---------+ | -1 | 0 | 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)   复制代码 代码如下:     mysql> SELECT POW(3,2), POWER(3,2); +----------+------------+ | POW(3,2) | POWER(3,2) | +----------+------------+ | 9 | 9 | +----------+------------+ row in set (0.00 sec)