MODIFY COLUMN to varchar(191) from varchar(255) for utfbmb4

varchar-191-utf8mb4.sql

SELECT CONCAT('ALTER TABLE `', TABLE_NAME, '` ',
    GROUP_CONCAT(CONCAT('MODIFY COLUMN `', COLUMN_NAME, '` VARCHAR(191)')), ';') AS _alter
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'mydatabase'
  AND COLUMN_TYPE LIKE 'VARCHAR%'
  AND CHARACTER_MAXIMUM_LENGTH = 255
  AND CHARACTER_SET_NAME = 'utf8mb4'
GROUP BY TABLE_SCHEMA, TABLE_NAME;