Here’s one method of comparing strings by case in MySQL. You can use the md5 function to hash the string and compare to its lower case value.
This example is for checking for usernames that are not lower case in moodle.
select username, md5(username), md5(lower(username)) from mdl_user where deleted = 0 and suspended = 0 and md5(username) != md5(lower(username));
If the md5 hash when the string is lower cased is different to the current md5 hash you will get a result.