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.

If CHAR() is invoked from within the mysql client, binary strings
display using hexadecimal notation, depending on the value of the
--binary-as-hex. For more information about that option, see
https://dev.mysql.com/doc/refman/5.7/en/mysql.html.

URL: https://dev.mysql.com/doc/refman/5.7/en/string-functions.html

