LOG2
LOG2 is an extension function for MaxCompute V2.0 that returns the binary logarithm of number.
Syntax
double log2(<number>)Parameters
number: Required. A value of the DOUBLE, BIGINT, INT, SMALLINT, TINYINT, FLOAT, DECIMAL, or STRING data type.
Return value
A DOUBLE value is returned. If the value of number is NULL, NULL is returned. An error is reported if the value of number is 0 or a negative number.
Sample data
This section provides sample source data and examples for you to understand how to use the function. In this topic, a table named mf_math_fun_t is created and data is inserted into the table. Sample statements:
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');Query data from the mf_math_fun_t table. Sample statement:
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 |
+------------+-------------+-------------+--------------+------------+-------------+Examples with static data
-- Returns NULL.
select log2(null);
-- Returns 0.0.
select log2(1);
-- Returns 3.0.
select log2(8);Examples with table data
Based on the sample data, you can calculate the binary logarithm of the values in all columns. The following command is an example:
-- Disable strict mode.
set odps.sql.udf.strict.mode=false;
-- Enable the new data types of MaxCompute V2.0. This command must be submitted together with the SQL statement.
set odps.sql.type.system.odps2=true;
select log2(int_data) as int_new, log2(bigint_data) as bigint_new, log2(double_data) as double_new, log2(decimal_data) as decimal_new, log2(float_data) as float_new, log2(string_data) as string_new from mf_math_fun_t;The following result is returned.
+--------------------+--------------------+----------------------+--------------------+----------------------+--------------------+
| int_new | bigint_new | double_new | decimal_new | float_new | string_new |
+--------------------+--------------------+----------------------+--------------------+----------------------+--------------------+
| NULL | NULL | -0.929610672108602 | -0.929610672108602 | -0.9296107376258038 | 3.3219280948873626 |
| NULL | NULL | NULL | NULL | NULL | NULL |
| NULL | NULL | NULL | 4.354028938054387 | NULL | 4.906890595608519 |
| NULL | 2.0 | -0.16812275880832692 | NULL | -0.16812278199699915 | NULL |
| 2.321928094887362 | NULL | NULL | NULL | NULL | 5.643856189774724 |
| NULL | 2.584962500721156 | 0.5849625007211562 | 0.5849625007211562 | 0.5849625007211562 | NULL |
| NULL | NULL | NULL | NULL | NULL | NULL |
| NULL | 0.0 | NULL | NULL | NULL | NULL |
| 3.1699250014423126 | NULL | 1.3673710656485296 | 1.3673710656485296 | 1.367371022986166 | NULL |
| NULL | 3.3219280948873626 | NULL | NULL | NULL | NULL |
+--------------------+--------------------+----------------------+--------------------+----------------------+--------------------+Related functions
LOG2 is a mathematical function. For more information about other mathematical functions, see Mathematical functions.