Syntax
HEX(str)
Purpose
HEX() converts a number or string str to a hexadecimal string. Each byte of each character in str is converted into two hexadecimal digits.
For a numeric parameter N, UNHEX(N) is not the reverse operation of HEX(N). In this case, you need to use CONV(HEX(N),16,10).
Examples
obclient> SELECT HEX(255), HEX('abc');
+----------+------------+
| HEX(255) | HEX('abc') |
+----------+------------+
| FF | 616263 |
+----------+------------+
1 row in set