MySQL学习笔记18：数学函数

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

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)