New answers tagged application-pages
You can create a WCF service layer which basically talks CRUD to your SQL database tables. Once this is in place you can use service calls from SharePoint. Later once you move to SP online expose the on premise WCF to internet. Make sure you have proper authentication in place. Alternatively you can make use of Azure.
you could use the Business Connectivity Services - BCS. It allows you to create CRUD operations based on and connected to external databases. msdn Link
You can only edit site pages(resides in content DB) using SPD.
The possibility of this to happen is may be your old solution still exist in your site collection.Try deactivating it and activate your new solution. Please let me know if this helped you or not or you are facing some other issue. Thanks
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