Forum Need to clear 'birthday' fields in my database
 

I have just migrated from phpbb2 where I was using birthday mod. I have noticed that now after migration 'birthday' fields in the database have got wrong format. I need to clear all these fields now but there are hundreds of them and deleting them one by one would take ages. What is the sql command to do so?

EDIT:

the command is:
Code:
update user set birthday=""