Searching filenames with different notation

Hi Folks, a problem that I could not solve yet. I have file with names like "songtitle.mp3" and other ones with file names like "artist - songtitle.mp3". Most of my files are like "artist - songtitle.mp3" but there are still thousands of files written incorrectly as "songtitle.mp3". How can I find only those files, which are written as "songtitle.mp3", just to change the file names manually?

Looks to me like the ones that you are looking for do not have the hyphen as part of the name, so perhaps this filter works:
NOT %_filename% HAS " - "

I don't understand why you want to find them.
Mp3Tag is a software to tag files with metadata.
So do you have content in the tagfields TITLE and ARTIST?
If so just buld new filenames with the converter Tag->Filename and the format string:
%artist% - %title%

If one of your tagfields has no content just filter:
%artist% MISSING
or
%title% MISSING

Works fine, thanks. Vielen Dank!

Have tried your propsal, works well. Thanks.