Syntax:
CHAR(N,... [USING charset_name])

CHAR() interprets each argument N as an integer and returns a string
consisting of the characters given by the code values of those
integers. NULL values are skipped.
By default, CHAR() returns a binary string. To produce a string in a
given character set, use the optional USING clause:

MariaDB> SELECT CHARSET(CHAR(0x65)), CHARSET(CHAR(0x65 USING utf8));
+---------------------+--------------------------------+
| CHARSET(CHAR(0x65)) | CHARSET(CHAR(0x65 USING utf8)) |
+---------------------+--------------------------------+
| binary              | utf8                           |
+---------------------+--------------------------------+

If USING is given and the result string is illegal for the given
character set, a warning is issued. Also, if strict SQL mode is
enabled, the result from CHAR() becomes NULL.

URL: https://mariadb.com/kb/en/char-function/

