A card grid has to know how much of an album is here — an album held 2
tracks of 10 wearing the same green tick as one held whole is the
complaint the badge-accuracy work was filed about — and
`GetAlbumCompleteness` is one query per album, which is fifty round
trips for a grid of fifty.
`GetAlbumsCompleteness` is the same question over a slice. It is two
grouping levels rather than the single-album form's correlated
subqueries, because a correlated subquery in the FROM clause is not
something SQLite will reliably do, and because the slice may only be
spelled once or sqlc expands it twice with independently numbered
placeholders.
An album with no files is absent from the result rather than zeroed:
"I have none of this" and "I have no idea" are the third state `Known`
exists to keep apart.
The test that matters is that the two spellings never disagree — they
are genuinely different SQL, so the risk is a drift in meaning (a
disc's total counted once per file, a duplicate counted twice) rather
than a typo.
logan
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