SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 1000 bytes (SQL: alter table users add unique `users_email_unique_

unique(email_unique`))

al poner php artisan me sale lo anterior, y me sale error,; porque sale este error?

SQLSTATE[42000]: Syntax error or access violation: 1071 Specified key was too long; max key length is 1000 bytes (SQL: alter table users add unique `users_email_unique_

unique(email_unique`))

al poner php artisan me sale lo anterior, y me sale error,; porque sale este error?