Will I lose my databases if I upgrade SQL Server 2012 Express to Standard?

In theory you will not have problems, there is full compatibility.

But if you are unsure, take a test first to be sure. In fact you can lose by wrong maneuvers. So it's good to be careful, to test before in an out-of-production environment, to have backup if you need to go back.

No.

This link teaches you how to do the installation steps . In any case, I recommend a backup of schema + data. There is a step-by-step to this here .

Every time I've installed different versions of SQL Server, side-by-side, they have always coexisted without touching each other's data. In fact, have you ever imagined how many distracted people would accidentally lose their data if that were not the case? The fury of the DBAs against Microsoft? :)

But already the saying goes, sure died of old .

Although all manuals, explanations and tests work without losing data, you should do what is always recommended for database maintenance: backup .

The real world is cruel and, no matter how hard you try to follow the right steps to not lose your data (completely or partially), Murphy's Law is our eternal adversary and one day it comes into play. >

It is recommended not only to back up your database but also to test the restore procedure on a regular basis so as not to find that backups are not only useful when you need them.