Change collation of a column in a table (mysql)

ALTER TABLE wp_posts2 MODIFY post_name VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;

 ALTER TABLE wp_posts2 MODIFY post_title VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_general_ci;

ALTER TABLE wp_posts2 MODIFY to_ping VARCHAR(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci;