convert all tables to new collate

SET @database = "database name";

SET @charset = "utf8mb4";

SET @collate = "utf8mb4_unicode_520_ci";

SELECT "SET foreign_key_checks = 0;"
UNION ALL
SELECT concat(
  "ALTER DATABASE `",
  `SCHEMA_NAME`,
  "` CHARACTER SET = ",
  @charset,
  " COLLATE = ",
  @collate,
  ";"
) AS `sql`
FROM `information_schema`.`SCHEMATA`
WHERE `SCHEMA_NAME` = @database
  AND (
    `DEFAULT_CHARACTER_SET_NAME` <> @charset
    OR `DEFAULT_COLLATION_NAME` <> @collate
  )
UNION ALL
SELECT concat(
  "ALTER TABLE `",
  `TABLE_SCHEMA`,
  "`.`",
  `TABLE_NAME`,
  "` CONVERT TO CHARACTER SET ",
  @charset,
  " COLLATE ",
  @collate,
  ";"
) AS `sql`
FROM `information_schema`.`TABLES`
WHERE `TABLE_SCHEMA` = @database
  AND `TABLE_TYPE` = "BASE TABLE"
  AND `TABLE_COLLATION` <> @collate
UNION ALL
SELECT concat(
  "ALTER TABLE `",
  c.`TABLE_SCHEMA`,
  "`.`",
  c.`TABLE_NAME`,
  "` CHANGE `",
  c.`COLUMN_NAME`,
  "` `",
  c.`COLUMN_NAME`,
  "` ",
  c.`COLUMN_TYPE`,
  " CHARACTER SET ",
  @charset,
  " COLLATE ",
  @collate,
  if(c.`IS_NULLABLE`="YES", " NULL", " NOT NULL"),
  ";"
) AS `sql`
FROM `information_schema`.`COLUMNS` c,
  `information_schema`.`TABLES` t,
  `information_schema`.`COLLATION_CHARACTER_SET_APPLICABILITY` a
WHERE c.`TABLE_SCHEMA` = t.`TABLE_SCHEMA`
  AND c.`TABLE_NAME` = t.`TABLE_NAME`
  AND t.`TABLE_COLLATION` = a.`COLLATION_NAME`
  AND c.`TABLE_SCHEMA` = @database
  AND c.`DATA_TYPE` IN (
    'varchar',
    'char',
    'text',
    'tinytext',
    'mediumtext',
    'longtext'
  )
  AND (
    c.`CHARACTER_SET_NAME` <> a.`CHARACTER_SET_NAME`
    OR c.`COLLATION_NAME` <> t.`TABLE_COLLATION`
  )
  AND t.`TABLE_TYPE` = "BASE TABLE"
UNION ALL
SELECT "SET foreign_key_checks = 1;";

copy the result and execute