HEX(str), HEX(N)
SELECT X'616263', HEX('abc'), UNHEX(HEX('abc'));
'abc', 616263, 'abc'
SELECT HEX(255), CONV(HEX(255),16,10);
'FF', 255
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.
SELECT X'616263', HEX('abc'), UNHEX(HEX('abc'));
'abc', 616263, 'abc'
SELECT HEX(255), CONV(HEX(255),16,10);
'FF', 255