MySQL函數學習筆記一：數學函數

MySQL函數學習筆記一：數學函數

1. ABS(x): 返回x的絕對值

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

2. PI(): 返回圓周率

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

3. SQRT(x): 返回x的平方根，要求（x為非負數，返回NULL）
mysql> select SQRT(49), SQRT(0), SQRT(-49);
+----------+---------+-----------+
| SQRT(49) | SQRT(0) | SQRT(-49) |
+----------+---------+-----------+
| 7 | 0 | NULL |
+----------+---------+-----------+

4. MOD(x,y): 求余函數，返回x被y除後的余數；對於帶有小數部分的數據值也起作用，它返回除法運算後的精確余數。

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的最小整數值，返回值轉為一個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):返回不大於X的最大整數值，返回值轉為一個BIGINT.

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

8. RAND()和RAND(X)

RAND(X) 返回一個隨機浮點值，范圍在０～１之間，X為整數，它被稱作種子值，用來產生重復序列。即當Ｘ值相同時，產生的隨機數也相同；

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(): 不帶參數的RAND()每次產生不同０～１之間的隨機數

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

9. ROUND(X)和ROUND(X,Y): 四捨五入函數，對Ｘ值按照Ｙ進行四捨五入，Ｙ可以省略，默認值為０;若Ｙ不為０，則保留小數點後面指定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): 與ROUND(X,Y)功能類似，但不進行四捨五入，只進行截取。

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): 返回參數Ｘ的符號，Ｘ的值為負、零或正數時返回結果依次為－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)與POWER(X,Y)功能相同，用於返回Ｘ的Ｙ次乘方的結果值

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乘方後的值:

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): 對數運算函數（Ｘ必須為正數），LOG(X)-返回Ｘ的自然對數(X相對於基數e的對數)　LOG10(X)-返回x的基數為10的對數：

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): 角度與弧度轉換函數

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): 正弦函數，其中Ｘ為弧度值

ASIN(X): 反正弦函數　其中Ｘ必須在－１到１之間

COS(X): 余弦函數，其中Ｘ為弧度值

ACOS(X): 反余弦函數　其中Ｘ必須在－１到１之間

TAN(X): 正切函數，其中Ｘ為弧度值

ATAN(X): 反正切函數，ATAN(X)與TAN(X)互為反函數

COT(X):　余切函數，函數COT和TAN互為倒函數

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 |
+--------------+--------------------+-----------+-------------------+--------------------+--------------------+-------------------+