https://mathiasbynens.be/notes/mysql-utf8mb4
https://dba.stackexchange.com/questions/8239/how-to-easily-convert-utf8-tables-to-utf8mb4-in-mysql-5-5

先把資料庫轉成utf8mb4
再把table轉成utf8mb4
再把column轉成utf8mb4

# For each database:
ALTER DATABASE database_name CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;
# For each table:
ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

# For each column:
use information_schema;
SELECT concat("ALTER DATABASE `",table_schema,"` CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;") as _sql FROM `TABLES` where table_schema like "yourDbName" group by table_schema;
SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name,"` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql FROM `TABLES` where table_schema like "yourDbName" group by table_schema, table_name;
SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type,"(",character_maximum_length,") CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql FROM `COLUMNS` where table_schema like "yourDbName" and data_type in ('varchar');
SELECT concat("ALTER TABLE `",table_schema,"`.`",table_name, "` CHANGE `",column_name,"` `",column_name,"` ",data_type," CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;") as _sql FROM `COLUMNS` where table_schema like "yourDbName" and data_type in ('text','tinytext','mediumtext','longtext');