ALTER  DATABASE  database_name  CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;

ALTER TABLE   table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

ALTER TABLE table_name CHANGE json_content json_content VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

SET NAMES 'utf8mb4';