Как перейти с utf8 на utf8mb4 в MySQL?
При такой конфигурации[mysqld]
init_connect='SET collation_connection = utf8mb4_unicode_ci'
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci

[client]
default-character-set = utf8mb4
имеем+--------------------------+--------------------+
| Variable_name                  | Value                       |
+------------------------------+------------------------+
| character_set_client          | utf8mb4                  |
| character_set_connection | utf8mb4                  |
| character_set_database    | utf8mb4                  |
| character_set_filesystem  | binary                      |
| character_set_results       | utf8mb4                   |
| character_set_server        | utf8mb4                   |
| character_set_system       | utf8                          |
| collation_connection        | utf8mb4_general_ci |
| collation_database          | utf8mb4_unicode_ci |
| collation_server               | utf8mb4_unicode_ci |
+-----------------------------+------------------------+
10 rows in set (0.01 sec)
По минимуму достаточно сменить charset одного поля в таблицеALTER TABLE `table` 
  MODIFY `description` VARCHAR(xxx) CHARACTER SET utf8mb4;
Ну или сразу у всех текстовых полей в таблицеALTER TABLE `table` CONVERT TO CHARACTER SET utf8mb4;