NOTE: The Generic SQL answer is Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='
This question is specific to rails/active-record, when you have:
ActionView::Template::Error: Mysql2::Error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT)
The accepted answer says to COLLATE
but I was hoping for some examples specific to rails.