Different DB size after backup?

Question

MySQL

Why might the sizes of the database differ after (export -> import) . The number of lines is the same, the types are the same, but the size is different.

Answer 1

Yes, lots of reasons.
If you back up the file, the size must be identical, otherwise it is a broken file.
If the backup is carried out by the mechanisms of the database itself, the size will differ in the vast majority of cases, because it will be a completely different file after restoration.