返回函数MySQL学习笔记18：数学函数 返回函数

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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)返回大于或于等x的最小数整

    FLOOR(x)返回小于或于等x的最大数整

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)      

    每日一道理

自己把自己说服了，是一种理智的胜利；自己被自己感动了，是一种心灵的升华；自己把自己征服了，是一种人生的成功。

RAND()和RAND(x)这两个函数失丢返回0～1的随机数

    区分在于，RAND()返回的数是完整随机的，而RAND(x)在x同相时返回的值同相

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近最的数整，也就是对x停止四舍五入处置

    ROUND(x,y)返回x留保到小数点后y位的值，在截取时停止四舍五入处置

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留保到小数点后y位的值，不停止四舍五入操纵

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为正数，0变不，1为数整

幂算运函数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)      

文章结束给大家分享下程序员的一些笑话语录： 祝大家在以后的日子里. 男生象Oracle般健壮; 女生象win7般漂亮; 桃花运象IE中毒般频繁; 钱包如Gmail容量般壮大, 升职速度赶上微软打补丁 ， 追女朋友像木马一样猖獗， 生活像重装电脑后一样幸福， 写程序敲代码和聊天一样有**。