Mass update users based on userfield value

[t3nt3tion]

I`m trying to move users from registered members usergroup to a usergroup I created based on a custom field value, and i`d like to do this with a SQL statement, particularly this one :

update user set usergroupid = 10 where userid in
(select userid from user
inner join userfield on
user.userid = userfield.userid
where userfield.field7 = 'valueinputedbyme');

Thing is I`m receiving a "userid" ambigous field error ...
Waiting for your replies

And yes, I know this has been asked a few times, but I didn`t see any "finishing" replies that something actually worked.