SELECT * FROM `first` as t1
LEFT JOIN `second` as t2 ON t1.id = t2.number_id
Error Code: 1267. Illegal mix of collations (utf8_general_ci,IMPLICIT) and (utf8_unicode_ci,IMPLICIT) for operation '=' 0.016 sec
SELECT * FROM `first` as t1
LEFT JOIN `second` as t2 ON t1.id COLLATE utf8_unicode_ci = t2.number_id COLLATE utf8_unicode_ci;