CHAR FUNCTION

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:

mysql> SELECT CHARSET(CHAR(X'65')), CHARSET(CHAR(X'65' USING utf8));
+----------------------+---------------------------------+
| CHARSET(CHAR(X'65')) | CHARSET(CHAR(X'65' 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://dev.mysql.com/doc/refman/8.0/en/string-functions.html