MySQL Tutorial/Math Numeric Functions/LOG

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LOG(X), LOG(B,X): If called with one parameter, this function returns the natural logarithm of X

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mysql> mysql> SELECT LOG(2); +------------------+ | LOG(2) | +------------------+ | 0.69314718055995 | +------------------+ 1 row in set (0.00 sec) mysql> mysql> SELECT LOG(-2); +---------+ | LOG(-2) | +---------+ | NULL | +---------+ 1 row in set (0.00 sec) mysql></source>


Using LOG with data in a table

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mysql> mysql> mysql> create table myTable(

   ->   id           int(2),
   ->   value        FLOAT(6,2)
   -> );

Query OK, 0 rows affected (0.03 sec) mysql> mysql> insert into myTable(ID, value)values (1,9); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (2,2.11); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (3,3.44); Query OK, 1 row affected (0.02 sec) mysql> insert into myTable(ID, value)values (4,-4.21); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (5,10); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (6,3); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (7,-5.88); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (8,123.45); Query OK, 1 row affected (0.01 sec) mysql> insert into myTable(ID, value)values (9,98.23); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (10,938.23); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (11,-984.23); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (12,198.23); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (13,-928.87); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (14,25.37); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (15,-918.3); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (16,9.23); Query OK, 1 row affected (0.00 sec) mysql> insert into myTable(ID, value)values (17,-8.23); Query OK, 1 row affected (0.00 sec) mysql> mysql> select * from myTable; +------+---------+ | id | value | +------+---------+ | 1 | 9.00 | | 2 | 2.11 | | 3 | 3.44 | | 4 | -4.21 | | 5 | 10.00 | | 6 | 3.00 | | 7 | -5.88 | | 8 | 123.45 | | 9 | 98.23 | | 10 | 938.23 | | 11 | -984.23 | | 12 | 198.23 | | 13 | -928.87 | | 14 | 25.37 | | 15 | -918.30 | | 16 | 9.23 | | 17 | -8.23 | +------+---------+ 17 rows in set (0.00 sec) mysql> mysql> select value, LOG(value) from myTable; +---------+------------------+ | value | LOG(value) | +---------+------------------+ | 9.00 | 2.1972245773362 | | 2.11 | 0.74668789777036 | | 3.44 | 1.2354714880192 | | -4.21 | NULL | | 10.00 | 2.302585092994 | | 3.00 | 1.0986122886681 | | -5.88 | NULL | | 123.45 | 4.8158361910706 | | 98.23 | 4.587311701861 | | 938.23 | 6.8439951006905 | | -984.23 | NULL | | 198.23 | 5.2894279511491 | | -928.87 | NULL | | 25.37 | 3.2335674066909 | | -918.30 | NULL | | 9.23 | 2.2224589989196 | | -8.23 | NULL | +---------+------------------+ 17 rows in set (0.00 sec) mysql> mysql> drop table myTable; Query OK, 0 rows affected (0.00 sec) mysql></source>