NOT LIKE not working in MySQL with Rails

Question

>> Comment.count
  SQL (0.3ms)   SELECT count(*) AS count_all FROM `comments` 
=> 451
>> Comment.count(:conditions => ["author_website not like ?",'aaaa'])
  SQL (1.4ms)   SELECT count(*) AS count_all FROM `comments` WHERE (author_website not like 'aaaa') 
=> 203
>> Comment.count(:conditions => ["author_website like ?",'aaaa'])
  SQL (1.2ms)   SELECT count(*) AS count_all FROM `comments` WHERE (author_website like 'aaaa') 
=> 0
>>

I was expecting the count of NOT LIKE to be 451.

I am using MySQL and Ruby on Rails.

Answer 1

Is author_website a nullable field?

If 248 rows had null values, this might explain it.

Could you do this instead?

Comment.count(:conditions => ["not(author_website like ?)",'aaaa'])

Answer 2

As troelskn is implying with his comment, if a value is NULL then it is neither like nor not like any particular value. Try:

Comment.count(:conditions => ["author_website is null OR author_website not like ?", 'aaaa'])