 the function returns NULL and (as\nof MySQL 5.7.4) a warning "Invalid argument for logarithm" is reported.\n\nURL: http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html\n\n','mysql> SELECT LN(2);\n        -> 0.69314718055995\nmysql> SELECT LN(-2);\n        -> NULL\n','http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html');
