How to connect Unity Android app with MS SQL server

I am trying to build an android application from Unity to connect with a MS SQL server database. I have found some approaches that worked on editor, mostly based on directly connecting from Unity to SQL server. However, this approach does not work when I build the android app. I only need to perform "select" (to login) and "insert" (to insert session data). Can you guys give some tips on the best way to do it? In addition, I thought maybe using a web service could be necessary, but I haven't found many examples using ASP.NET as intermediary web server.