Syntax:
HEX(str), HEX(N)

For a string argument str, HEX() returns a hexadecimal string
representation of str where each byte of each character in str is
converted to two hexadecimal digits. (Multibyte characters therefore
become more than two digits.) The inverse of this operation is
performed by the UNHEX() function.

For a numeric argument N, HEX() returns a hexadecimal string
representation of the value of N treated as a longlong (BIGINT) number.
This is equivalent to CONV(N,10,16). The inverse of this operation is
performed by CONV(HEX(N),16,10).

For a NULL argument, this function returns NULL.

URL: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html

