Enhancement

This is a bad user experience as the index prefix is specified in characters, but the limit in the error message is in bytes.

Here 1000 characters is 4000 bytes as UTF-8 takes up to 4 bytes per character.

sql> CREATE TABLE t1(id int primary key, c1 text, key(c1(1000)));
ERROR: 1071 (42000): Specified key was too long; max key length is 3072 bytes