MaxCompute:LOG

Syntax

double log(<base>, <x>)

Parameters

Return value

Returns a DOUBLE value. Returns null under the conditions listed in Usage notes.

Usage notes

• If base or x is null, null is returned.

• If base or x is a negative number or 0, null is returned.

• If base is 1, null is returned. A base of 1 causes division by zero.

Examples

The following examples use the mf_math_fun_t table. To create and populate this table, run:

create table if not exists mf_math_fun_t(
     int_data     int,
     bigint_data  bigint,
     double_data  double,
     decimal_data decimal,
     float_data   float,
     string_data  string
    );
insert into mf_math_fun_t values
(null, -10, 0.525, 0.525BD, cast(0.525 as float), '10'),
(-20, null, -0.1, -0.1BD, cast(-0.1 as float), '-10'),
(0, -1, null, 20.45BD, cast(-1 as float), '30'),
(-40, 4, 0.89, null, cast(0.89 as float), '-30'),
(5, -50, -1, -1BD, null, '50'),
(-60, 6, 1.5, 1.5BD, cast(1.5 as float), '-50'),
(-1, -70, -7.5, -7.5BD, cast(-7.5 as float),null ),
(-80, 1, -10.2, -10.2BD, cast(-10.2 as float), '-1' ),
(9, -90, 2.58, 2.58BD, cast(2.58 as float), '0'),
(-100, 10, -5.8, -5.8BD, cast(-5.8 as float), '-90');

To view the table data, run:

select * from mf_math_fun_t;
-- The following result is returned:
+------------+-------------+-------------+--------------+------------+-------------+
| int_data   | bigint_data | double_data | decimal_data | float_data | string_data |
+------------+-------------+-------------+--------------+------------+-------------+
| NULL       | -10         | 0.525       | 0.525        | 0.525      | 10          |
| -20        | NULL        | -0.1        | -0.1         | -0.1       | -10         |
| 0          | -1          | NULL        | 20.45        | -1.0       | 30          |
| -40        | 4           | 0.89        | NULL         | 0.89       | -30         |
| 5          | -50         | -1.0        | -1           | NULL       | 50          |
| -60        | 6           | 1.5         | 1.5          | 1.5        | -50         |
| -1         | -70         | -7.5        | -7.5         | -7.5       | NULL        |
| -80        | 1           | -10.2       | -10.2        | -10.2      | -1          |
| 9          | -90         | 2.58        | 2.58         | 2.58       | 0           |
| -100       | 10          | -5.8        | -5.8         | -5.8       | -90         |
+------------+-------------+-------------+--------------+------------+-------------+

-- The return value is 4.0.
select log(2, 16);
-- The return value is null.
select log(2, null);

select log(2,bigint_data) as bigint_new, log(2,double_data) as double_new, log(2,decimal_data) as decimal_new, log(2,string_data) as string_new from mf_math_fun_t;

+--------------------+----------------------+--------------------+--------------------+
| bigint_new         | double_new           | decimal_new        | string_new         |
+--------------------+----------------------+--------------------+--------------------+
| NULL               | -0.929610672108602   | -0.929610672108602 | 3.3219280948873626 |
| NULL               | NULL                 | NULL               | NULL               |
| NULL               | NULL                 | 4.354028938054387  | 4.906890595608519  |
| 2.0                | -0.16812275880832692 | NULL               | NULL               |
| NULL               | NULL                 | NULL               | 5.643856189774724  |
| 2.584962500721156  | 0.5849625007211562   | 0.5849625007211562 | NULL               |
| NULL               | NULL                 | NULL               | NULL               |
| 0.0                | NULL                 | NULL               | NULL               |
| NULL               | 1.3673710656485296   | 1.3673710656485296 | NULL               |
| 3.3219280948873626 | NULL                 | NULL               | NULL               |
+--------------------+----------------------+--------------------+--------------------+

Related functions

LOG is a mathematical function. For more information, see Mathematical functions.