Wrong subquery

I’m using Linq2Db v5.2.2 in a .NET7.0 project. I have this code

await using var db = new Database.Database();

var pcScanHdd = GetPcScanId(db, ScanFlags.HardDisks);
//var a = await pcScanHdd.ToListAsync();

var query =
	from ps in pcScanHdd
	join pc in db.Pcs on ps.PcId equals pc.Id
	join scan in db.Scan on ps.ScanId equals scan.Id
	join disk in db.LogicalHdds on scan.Id equals disk.ParentId
	where disk.MediaType == MediaTypeEnum.FixedHardDisk
		  && disk.DriveType == DriveTypeEnum.LocalDisk
	select new { pc, scan, disk };

GetPcScanId is a function returning an IQueryable<PcScanId> where PcScanId is defined as

private record PcScanId
{
	public int PcId;
	public int ScanId;
}

var pcScanHdd = GetPcScanId(db, ScanFlags.HardDisks) returns this query

SELECT
	pc.id,
	Max(scan_1.id)
FROM
	scan scan_1
		INNER JOIN pcs pc ON scan_1.id_parent = pc.id
WHERE
	pc.endDate IS NULL AND @flags = (scan_1.flags & @flags_1)
GROUP BY
	pc.id

If I try var a = await pcScanHdd.ToListAsync(); I get correct result. Unfortunately when I use pcScanHdd in the next query, subquery is completely wrong:

FROM
	(
		SELECT
			0 as PcId
		FROM
			scan scan_1
				INNER JOIN pcs pc ON scan_1.id_parent = pc.id
		WHERE
			pc.endDate IS NULL AND @flags = (scan_1.flags & @flags_1)
		GROUP BY
			pc.id
	) ps
		INNER JOIN pcs pc_1 ON ps.PcId = pc_1.id
		INNER JOIN scan scan_2 ON ps.PcId = scan_2.id
		INNER JOIN info_logicaldisk disk ON scan_2.id = disk.id_parent
WHERE
	disk.MediaType = 12 AND disk.DriveType = 3

SELECT 0 as PcId is bad, but INNER JOIN scan scan_2 ON ps.PcId = scan_2.id is a nonsense. I can’t understand why it works if I execute the query itself, but it goes bad when I use it in another query.

[sdanyliv]

Well it is doable in different way:

var query = 
	from pc in db.Pcs
	from scan in pc.Scans
		.Where(scan => pc.DismissedDate == null && (scan.Flags & flags) == flags)
		.OrderByDescending(scan => scan.scanId)
		.Take(1)
	select new 
	{
		pc,
		lastScan = scan
	};

[mark74]

Seems like with your updated query it’s working. Let me test it some more… and thank you 😃