I'm surprised to discover there's no official way to change the location of the database (I'm on Windows).
I have my data backed up from various locations on my drive and I want to put my database in one of them. Without data backup, anything that's in Joplin should be considered expendable, which isn't what I want.
About Backup, normally you'd sync to somewhere, like another drive, ex: S:\Joplin or a Network drive like \MyServer\Backup\Joplin.
This way, the sync keeps a permanent backup.
I don't know if you can change in a config the local folder on Windows (which one, 7, 8.1, 10?) - but if you really want this you could use a Junction to link the local .config folder to another drive... Again, how to set it up depends the Windows version.
But IMHO the easiest is the filesystem sync - see above.
Don't you backup your user folder? Because everything is in there, under .config
No, syncing is not a backup solution. Do not use it as such!
If something happens to your sync location your local data will be lost! There's no master/server and slave/client concept. It's a 2-way sync.
Thanks! You're very certainly right @tessus - and I do use export to JEX (but I also backup the sync folder) 
But anyway it wasn't the OP's question, in fact.
Edit: I could restore the local folder even if I'd loose everything on one PC as I've the same app and config on a few PCs (syncing to a network drive), so I just would have to restore the local .config from another PC. I guess, anyway...
Why answer this 3 months later? (and I've deleted my own answer as --profile is actually an unsupported flag)
today I ran into the same issue as the thread starter. And after I found your profile switch solution I posted it here so other people like me could find it more easily
In my case I don't want to have the user data in $HOME/.config (linux) - because in this location I store configuration data only. The .config directory doesn't contain any sensitive data - and I want to keep it that way.
Therefore I like to have all my private user data at another location. That location is encrypted with another security key and other backup intervals (and locations) apply.
If you remove the --profile switch I have to workaround this by symlinking .config/joplin-desktop to my secure user data location. That would be an ugly solution.
P.S.: IMHO it would be better if the database location can be configured in Joplin's settings.
Hmm, the settings are stored in the database....
Not really. That's why there are sym links on Linux. Also, this setup would be supported.