mysql-error-1071

#1071 - Specified key was too long; max key length is 767 bytes

When I executed the following command: ALTER TABLE `mytable` ADD UNIQUE ( `column1` , `column2` ); I got this error message: #1071 - Specified key was too long; max key length is 767 bytes Information about column1 and column2: column1 varchar(20) utf8_general_ci column2 varchar(500) utf8_general_ci I think varchar(20) only req...