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(email)) - PHP

When you encounter the above error message, it means that you have tried to create a unique key constraint on a column that exceeds the maximum allowed length of 1000 bytes.

This error can occur when creating a unique index on a VARCHAR or TEXT field that has a high character limit. To fix this issue, you can either reduce the length of the field, or specify a prefix length for the index.

The following code snippet shows an example of how to set a prefix length for the index:

ALTER TABLE `users`
ADD UNIQUE KEY `users_email_unique` (`email`(100));

In this example, we have set a prefix length of 100 for the email field. This will create a unique index that only uses the first 100 characters of the field.

Note that reducing the length of the field or setting a prefix length for the index may affect the uniqueness of the key. Therefore, it is important to review your database schema and application requirements before making any changes.