The UPPER function converts all lowercase characters in a value
    expression to uppercase characters. This function is useful to
    maintain consistency in value expressions in the database.

    If the result of the value expression is NULL, the function
    returns a null value.

    When you use the UPPER function, SQL follows the rules of
    the character set of the value expression when converting
    characters to uppercase. For example, if the character set of
    the value expression is Hanzi and ASCII, SQL converts only the
    ASCII characters to uppercase. It does not convert the Hanzi
    characters.