MySQL/MariaDB utf8 is not real UTF-8 — use utf8mb4

Inserting emojis or certain Unicode characters fails with 'Incorrect string value' error. The column charset is set to utf8 but certain characters are rejected.

MySQL utf8 charset only supports up to 3 bytes per character (Basic Multilingual Plane only). Emojis and many symbols require 4 bytes. Use utf8mb4 charset and utf8mb4_unicode_ci collation instead. ALTER TABLE: ALTER TABLE t CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci. Also update connection string to specify charset=utf8mb4.

MySQL created utf8 as a 3-byte encoding for performance reasons. When true UTF-8 (4 bytes) was needed later, they could not change utf8 without breaking compatibility, so they created utf8mb4.