Azure offers an In App MySQL database for developers using an App Service plan. This enables developers to run a MySQL database within the same environment that hosts their web app.
Microsoft sate that the in-app MySQL service is not intended for production use. However, for smaller sites it can be a cost effective solution.
Occasionally, in-app databases can crash or get corrupted. If this happens launch phpMyAdmin by clicking the "Manage" link within your Azure Portal...
Once loaded, select your database and click the "check all" checkbox to select all tables. Then select "Check Table".
If any tables show as crashed or corrupted you can then select the damaged table and execute the "Repair table" command.
Hopefully, this will fix your table and get your site back up and running again. Good luck!