MySQL won't properly GROUP BY on emojis

Question

I'm storing single emojis in a CHAR column in a MySQL database. The column's encoding is utf8mb4.

When I run this aggregate query, MySQL won't group by the emoji characters. It instead returns a single row with a single emoji and the count of all the rows in the database.

SELECT emoji, count(emoji) FROM emoji_counts GROUP BY emoji

Here's my table definition:

CREATE TABLE `emoji_counts` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `emoji` char(1) DEFAULT '',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

Is there some special Unicode behavior I'll have to account for?

Answer 1

Turns out I needed to specify an expanded collation in the query, namely utf8mb4_unicode_520_ci.

This worked:

SELECT emoji, count(emoji) FROM emoji_counts group by emoji collate utf8mb4_unicode_520_ci;

EDIT: That collation isn't available on some server configs (including ClearDB's)... utf8mb4_bin also appears to work.