Syntax:
UPPER(str)

Returns the string str with all characters changed to uppercase
according to the current character set mapping, or NULL if str is NULL.
The default character set is utf8mb4.

mysql> SELECT UPPER('Hej');
        -> 'HEJ'

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.

URL: https://dev.mysql.com/doc/refman/8.0/en/string-functions.html

