hex(n, bin, or str) - Convert the argument to hexadecimal 
If the argument is a string, returns two hex digits for each character in the string.
If the argument is a number or binary, returns the hexadecimal representation.
Example:
  > SELECT hex(17) FROM src LIMIT 1;
  'H1'
  > SELECT hex('Facebook') FROM src LIMIT 1;
  '46616365626F6F6B'