String Functions and Operators mysql>  SELECT UNHEX(’GG’); +-------------+ | UNHEX(’GG’) | +-------------+ | NULL | +-------------+ A  NULL  result can occur if the argument to  UNHEX()  is a  BINARY  column, because values are padded with  0x00  bytes when stored but those bytes are not stripped on retrieval. For example,  ’41’  is stored into a  CHAR(3)  column as  ’41 ’  and retrieved as  ’41’  (with the trailing pad space stripped), so UNHEX()  for the column value returns  X’41’ . By contrast,  ’41’  is stored into a  BINARY(3)  column as  ’41\0’  and retrieved as  ’41\0’  (with the trailing pad  0x00  byte not stripped).  ’\0’  is not a legal hexadecimal digit, so  UNHEX()  for the column value returns  NULL . For a numeric argument  N , the inverse of  HEX( N )  is not performed by  UNHEX() . Use CONV(HEX( N ),16,10)  instead. See the description of  HEX() . If  UNHEX()  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 Section 4.5.1, “mysql — The MySQL Command-Line Client” . See the description of  LOWER()  for information that also applies to  UPPER() . This included information about how to perform lettercase conversion of binary strings ( BINARY ,  VARBINARY ,  BLOB ) for which these functions are ineffective, and information about case folding for Unicode character sets. This function is multibyte safe. UCASE()  used within views is rewritten as  UPPER() 2184 Returns the string  str  with all characters changed to uppercase according to the current character set mapping. The default is  utf8mb4 . mysql>  SELECT UPPER(’Hej’); -> ’HEJ’ • UPPER( str )