Package 'mysql-server-5.7' has no installation candidate

As an AI language model, I do not have access to your system's package manager or repositories. However, "Package 'mysql-server-5.7' has no installation candidate" usually occurs when the package is not available in the repositories or the package name is incorrect.

To resolve this issue, you can try the following steps:

1. Update your package list by running the command:

   sudo apt update

2. Try installing the package again by running the command:

   sudo apt install mysql-server

3. If step 2 does not work, try adding the MySQL APT repository to your system by following the instructions in this link: https://dev.mysql.com/doc/mysql-apt-repo-quick-guide/en/

4. Once you have added the repository, update your package list by running the command:

   sudo apt update

5. Try installing the package again by running the command:

   sudo apt install mysql-server-5.7

If none of the above steps work, it is possible that the package is no longer available or has been deprecated. In this case, you may need to consider installing a different version of MySQL or a different database management system altogether.