MySQL函数学习笔记一:数学函数

1. ABS(x): 返回x的绝对值

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

2. PI(): 返回圆周率

mysql> select PI();
+----------+
| PI()     |
+----------+
| 3.141593 |
+----------+

3. SQRT(x): 返回x的平方根,要求(x为非负数,返回NULL)

mysql> select SQRT(49), SQRT(0), SQRT(-49);
+----------+---------+-----------+
| SQRT(49) | SQRT(0) | SQRT(-49) |
+----------+---------+-----------+
|        7 |       0 |      NULL |
+----------+---------+-----------+

4. MOD(x,y): 求余函数,返回x被y除后的余数;对于带有小数部分的数据值也起作用,它返回除法运算后的精确余数。

mysql> select MOD(31,8), MOD(21,-8), MOD(-7,2), MOD(-7,-2), MOD(45.5,6);
+-----------+------------+-----------+------------+-------------+
| MOD(31,8) | MOD(21,-8) | MOD(-7,2) | MOD(-7,-2) | MOD(45.5,6) |
+-----------+------------+-----------+------------+-------------+
|         7 |          5 |        -1 |         -1 |         3.5 |
+-----------+------------+-----------+------------+-------------+

5. CEIL(X): 返回不小X的最小整数值,返回值转为一个BIGINT.

mysql> select CEIL(-3.35), CEIL(3.35);
+-------------+------------+
| CEIL(-3.35) | CEIL(3.35) |
+-------------+------------+
|          -3 |          4 |
+-------------+------------+

6. CEILING(X): 同CEIL(X)

mysql> select CEILING(-3.35), CEILING(3.35);
+----------------+---------------+
| CEILING(-3.35) | CEILING(3.35) |
+----------------+---------------+
|             -3 |             4 |
+----------------+---------------+

7. FLOOR(X):返回不大于X的最大整数值,返回值转为一个BIGINT.

mysql> select FLOOR(-3.35), FLOOR(3.35);
+--------------+-------------+
| FLOOR(-3.35) | FLOOR(3.35) |
+--------------+-------------+
|           -4 |           3 |
+--------------+-------------+

8. RAND()和RAND(X)

RAND(X) 返回一个随机浮点值,范围在0~1之间,X为整数,它被称作种子值,用来产生重复序列。即当X值相同时,产生的随机数也相同;

mysql> select RAND(10), RAND(10), RAND(2), RAND(-2);
+--------------------+--------------------+--------------------+--------------------+
| RAND(10)           | RAND(10)           | RAND(2)            | RAND(-2)           |
+--------------------+--------------------+--------------------+--------------------+
| 0.6570515219653505 | 0.6570515219653505 | 0.6555866465490187 | 0.6548542125661431 |
+--------------------+--------------------+--------------------+--------------------+

RAND(): 不带参数的RAND()每次产生不同0~1之间的随机数

mysql> SELECT RAND(), RAND(), RAND();
+--------------------+--------------------+---------------------+
| RAND()             | RAND()             | RAND()              |
+--------------------+--------------------+---------------------+
| 0.6931893636409094 | 0.5147262984092592 | 0.49406343185721285 |
+--------------------+--------------------+---------------------+

9. ROUND(X)和ROUND(X,Y): 四舍五入函数,对X值按照Y进行四舍五入,Y可以省略,默认值为0;若Y不为0,则保留小数点后面指定Y位。

mysql> select ROUND(-1.14), ROUND(-1.9), ROUND(1.14), ROUND(1.9);
+--------------+-------------+-------------+------------+
| ROUND(-1.14) | ROUND(-1.9) | ROUND(1.14) | ROUND(1.9) |
+--------------+-------------+-------------+------------+
|           -1 |          -2 |           1 |          2 |
+--------------+-------------+-------------+------------+

mysql> select ROUND(1.38,1), ROUND(1.38,0), ROUND(232.38,-1), ROUND(232.38,-2);
+---------------+---------------+------------------+------------------+
| ROUND(1.38,1) | ROUND(1.38,0) | ROUND(232.38,-1) | ROUND(232.38,-2) |
+---------------+---------------+------------------+------------------+
|           1.4 |             1 |              230 |              200 |
+---------------+---------------+------------------+------------------+

10. TRUNCATE(X,Y): 与ROUND(X,Y)功能类似,但不进行四舍五入,只进行截取。

mysql> select TRUNCATE(1.33,1), TRUNCATE(1.99,1), TRUNCATE(1.99,0), TRUNCATE(19.99,-1);
+------------------+------------------+------------------+--------------------+
| TRUNCATE(1.33,1) | TRUNCATE(1.99,1) | TRUNCATE(1.99,0) | TRUNCATE(19.99,-1) |
+------------------+------------------+------------------+--------------------+
|              1.3 |              1.9 |                1 |                 10 |
+------------------+------------------+------------------+--------------------+

11. SIGN(X): 返回参数X的符号,X的值为负、零或正数时返回结果依次为-1,0或1mysql> select SIGN(-21), SIGN(-0),SIGN(0), SIGN(0.0), SIGN(21);

+-----------+----------+---------+-----------+----------+
| SIGN(-21) | SIGN(-0) | SIGN(0) | SIGN(0.0) | SIGN(21) |
+-----------+----------+---------+-----------+----------+
|        -1 |        0 |       0 |         0 |        1 |
+-----------+----------+---------+-----------+----------+

12. POW(X,Y), POWER(X,Y)和EXP(X)

POW(X,Y)与POWER(X,Y)功能相同,用于返回X的Y次乘方的结果值

mysql> select pow(2,2), pow(2,-2), pow(-2,2), pow(-2,-2);
+----------+-----------+-----------+------------+
| pow(2,2) | pow(2,-2) | pow(-2,2) | pow(-2,-2) |
+----------+-----------+-----------+------------+
|        4 |      0.25 |         4 |       0.25 |
+----------+-----------+-----------+------------+

mysql> select power(2,2), power(2,-2), power(-2,2), power(-2,-2);
+------------+-------------+-------------+--------------+
| power(2,2) | power(2,-2) | power(-2,2) | power(-2,-2) |
+------------+-------------+-------------+--------------+
|          4 |        0.25 |           4 |         0.25 |
+------------+-------------+-------------+--------------+

EXP(X): 返回e的X乘方后的值:

mysql> select EXP(3), EXP(0), EXP(-3);
+-------------------+--------+---------------------+
| EXP(3)            | EXP(0) | EXP(-3)             |
+-------------------+--------+---------------------+
| 20.08553692318767 |      1 | 0.04978706836786393 |
+-------------------+--------+---------------------+

13. LOG(X)和LOG10(X): 对数运算函数(X必须为正数),LOG(X)-返回X的自然对数(X相对于基数e的对数) LOG10(X)-返回x的基数为10的对数:

mysql> select LOG(-3), LOG(0), LOG(3), LOG10(-100), LOG10(0), LOG10(100);
+---------+--------+--------------------+-------------+----------+------------+
| LOG(-3) | LOG(0) | LOG(3)             | LOG10(-100) | LOG10(0) | LOG10(100) |
+---------+--------+--------------------+-------------+----------+------------+
|    NULL |   NULL | 1.0986122886681098 |        NULL |     NULL |          2 |
+---------+--------+--------------------+-------------+----------+------------+

14. RADIANS(X) 和 DEGREES(X): 角度与弧度转换函数

mysql> select RADIANS(90), RADIANS(180), DEGREES(PI()), DEGREES(PI()/2);
+--------------------+-------------------+---------------+-----------------+
| RADIANS(90)        | RADIANS(180)      | DEGREES(PI()) | DEGREES(PI()/2) |
+--------------------+-------------------+---------------+-----------------+
| 1.5707963267948966 | 3.141592653589793 |           180 |              90 |
+--------------------+-------------------+---------------+-----------------+

15. SIN(X), ASIN(X), COS(X), ACOS(X), TAN(X), ATAN(X), COT(X)

SIN(X): 正弦函数,其中X为弧度值

ASIN(X): 反正弦函数 其中X必须在-1到1之间

COS(X): 余弦函数,其中X为弧度值

ACOS(X): 反余弦函数 其中X必须在-1到1之间

TAN(X): 正切函数,其中X为弧度值

ATAN(X): 反正切函数,ATAN(X)与TAN(X)互为反函数

COT(X): 余切函数,函数COT和TAN互为倒函数

mysql> select SIGN(PI()/2),ASIN(1),COS(PI()), ACOS(-1), TAN(PI()/4), ATAN(1), COT(0.5);
+--------------+--------------------+-----------+-------------------+--------------------+--------------------+-------------------+
| SIGN(PI()/2) | ASIN(1)            | COS(PI()) | ACOS(-1)          | TAN(PI()/4)        | ATAN(1)            | COT(0.5)          |
+--------------+--------------------+-----------+-------------------+--------------------+--------------------+-------------------+
|            1 | 1.5707963267948966 |        -1 | 3.141592653589793 | 0.9999999999999999 | 0.7853981633974483 | 1.830487721712452 |
+--------------+--------------------+-----------+-------------------+--------------------+--------------------+-------------------+


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