2019-02-11, 11:28
All good advice from @Karellen. I can not get your db from that site (button says wait then does nothing). If you need me to point at specific issues in your tagging then put it somewhere simple e.g. Dropbox or google drive. Meanwhile I think I'm going to just let you fix your tagging 
But in summary reply to some of the questions that have come up:
You are seeing [missing] as an artist because one or more music files are not tagged with an artist. Kodi has [missing] artist entry so that all songs will have an artist and therefore we can avoid use of left joins which are slow. Not sure why you have a song id of -1, that is odd but I would sort out your tagging and start again with an empty db. Then see is the issue persists.
Yes there is some denormalisation in the db, a common physical implementation, but I promise there are no data inconsistencies. The song table has an strArtistDisp field because you could have tagged it with a complex/decorative artist name e.g. "artistA (feat artistB)" and along with an ARTISTS and/or mbid tags that allow Kodi to identify the individual artists. Then Kodi can display "artistA (feat artistB)" during playback, but have both "artistA" and "artistB" separately in the list of artists.
Kodi supports several ways of tagging songs with several artist credits. Historically it uses " / " space-slash-space as a separator for single frame tags (IDE v2.3), but not just "/" because of artists like "AC/DC". You can also use multiple frame tag formats e.g. FLAC file or v2.4 for mp3 to enter the multiple values. It also is Musicbrainzid enabled, hence using Picard to tag files with matched mbid and ARTISTS tags. Finally you can specify your own artist name spearators in advancedsettings.xml e.g. tell it to use ";". Take care here as some punctuation appears in individual artist names e.g. "Earth, Wind & Fire".
But in summary reply to some of the questions that have come up:
You are seeing [missing] as an artist because one or more music files are not tagged with an artist. Kodi has [missing] artist entry so that all songs will have an artist and therefore we can avoid use of left joins which are slow. Not sure why you have a song id of -1, that is odd but I would sort out your tagging and start again with an empty db. Then see is the issue persists.
Yes there is some denormalisation in the db, a common physical implementation, but I promise there are no data inconsistencies. The song table has an strArtistDisp field because you could have tagged it with a complex/decorative artist name e.g. "artistA (feat artistB)" and along with an ARTISTS and/or mbid tags that allow Kodi to identify the individual artists. Then Kodi can display "artistA (feat artistB)" during playback, but have both "artistA" and "artistB" separately in the list of artists.
Kodi supports several ways of tagging songs with several artist credits. Historically it uses " / " space-slash-space as a separator for single frame tags (IDE v2.3), but not just "/" because of artists like "AC/DC". You can also use multiple frame tag formats e.g. FLAC file or v2.4 for mp3 to enter the multiple values. It also is Musicbrainzid enabled, hence using Picard to tag files with matched mbid and ARTISTS tags. Finally you can specify your own artist name spearators in advancedsettings.xml e.g. tell it to use ";". Take care here as some punctuation appears in individual artist names e.g. "Earth, Wind & Fire".
