How to support full Unicode in MySQL databases

Change the character set and collation properties of the databases, tables, and columns to use utf8mb4 instead of utf8.
# For each database:
ALTER DATABASE database_name CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci;
# For each table:
ALTER TABLE table_name CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
# For each column:
ALTER TABLE table_name CHANGE column_name column_name VARCHAR(191) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
# (Don’t blindly copy-paste this! The exact statement depends on the column type, maximum length, and other properties. The above line is just an example for a `VARCHAR` column.)
Modify connection, client, and server character sets
In your application code, set the connection character set to utf8mb4. This can be done by simply replacing any variants of SET NAMES utf8 with SET NAMES utf8mb4. If your old SET NAMES statement specified the collation, make sure to change that as well, e.g. SET NAMES utf8 COLLATE utf8_unicode_ci becomes SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci.
Make sure to set the client and server character set as well. I have the following in my MySQL configuration file (/etc/my.cnf):
[client]
default-character-set = utf8mb4

[mysql]
default-character-set = utf8mb4

[mysqld]
character-set-client-handshake = FALSE
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci
You can easily confirm these settings work correctly:
mysql> SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
+--------------------------+--------------------+
| Variable_name            | Value              |
+--------------------------+--------------------+
| character_set_client     | utf8mb4            |
| character_set_connection | utf8mb4            |
| character_set_database   | utf8mb4            |
| character_set_filesystem | binary             |
| character_set_results    | utf8mb4            |
| character_set_server     | utf8mb4            |
| character_set_system     | utf8               |
| collation_connection     | utf8mb4_unicode_ci |
| collation_database       | utf8mb4_unicode_ci |
| collation_server         | utf8mb4_unicode_ci |
+--------------------------+--------------------+
10 rows in set (0.00 sec)
Repair and optimize all tables
mysqlcheck -u root -p --auto-repair --optimize --all-databases