I have updated from Kubuntu 17.10 to Kubuntu 18.4.
With the new version it is not possible to open an existing kmymoney sql-database. Any idea how to fix this or is this a bug in kmymoney?

Erich

Please provide some more information. What version of KMyMoney is it? Which sql are you using? Do you get any error message? If not, try running from a command line, as there may be more diagnostic output that way.

Separately, have you tried opening the database directly with sql? That would help determine if the problem is with the database itself (either the actual database, or the database software) or with how KMM is trying to access it.

It seems I have the same issue.
I worked before with Ubuntu 16.04 and KmyMoney 4.7 using MySQL database.
After I updated to Ubuntu 18.04 including KmyMoney 5.0 no option is available to change the database type from SQLite Version 3.0 to MySQL within the File - open database menu.
I just reinstalled MySQL-Server but without any success

after I installed the complete kubuntu-desktop the menu was available
but it doesn't work because of an qt error . . .

I"m not sure why I didn't see your previous post, but now, if you want any help, you need to provide some additional information - such as what is the error?

In terms of changing from SQLite to MySQL, I think it might be that you first need to save as a file, and then when you save as SQL you should have the choice of which sql engine to use.

It won't work with any of the released 5.0.[0-1] version. If you want to try, you need to use the appimage. But be aware that this is produced off the unstable master branch and you mileage may vary.