LOG

描述

返回基于底数b的x的对数。

语法

LOG(<b>[, <x>])

参数

参数	说明
<b>	底数 必须大于 0 且不等于 1
<x>	可选，真数必须大于 0，默认为自然数 e

返回值

返回一个浮点数。特殊情况：

• 当 b 为 NULL 或 x 为 NULL 时，返回NULL
• 当 任意一个参数 NaN 时，返回 NaN
• 当 参数不满足输入限制时，返回 NULL

举例

select log(5,1);

+---------------+
| log(5.0, 1.0) |
+---------------+
|             0 |
+---------------+

select log(3),ln(3);

+--------------------+--------------------+
| log(3)             | ln(3)              |
+--------------------+--------------------+
| 1.0986122886681098 | 1.0986122886681098 |
+--------------------+--------------------+

select log(3,20);

+--------------------+
| log(3.0, 20.0)     |
+--------------------+
| 2.7268330278608417 |
+--------------------+

select log(2,65536);

+-------------------+
| log(2.0, 65536.0) |
+-------------------+
|                16 |
+-------------------+

select log(5,NULL);

+------------------------------+
| log(cast(5 as DOUBLE), NULL) |
+------------------------------+
|                         NULL |
+------------------------------+

select log(NULL,3);

+------------------------------+
| log(NULL, cast(3 as DOUBLE)) |
+------------------------------+
|                         NULL |
+------------------------------+

select log(2 ,cast('nan' as double));

+-------------------------------+
| log(2 ,cast('nan' as double)) |
+-------------------------------+
|                           NaN |
+-------------------------------+

select log(2 ,-1);

+------------+
| log(2 ,-1) |
+------------+
|       NULL |
+------------+