Nesting multiple same select queries and reuse without second round trip to database - sql

Question

I am having a rows with two different IDs in database. Now I am trying to show two different data columns in one row, I tried something like this:
SELECT
[dbo].[fnHexToNumber]([Participant].[Stake]) AS [PlayerStake],
(SELECT [dbo].[fnHexToNumber]([Stake])
FROM [dbo].[Participant_Complete]
WHERE [ParticipantId] = [Fold].[HouseParticipantId]) AS [HouseStake],
([dbo].[fnHexToNumber]([Participant].[Stake]) + [dbo].[fnHexToNumber]([C].[RunningWinLoss])) AS [PlayerStakeAfterRound],
(SELECT [dbo].[fnHexToNumber]([Stake])
FROM [dbo].[Participant_Complete]
WHERE [ParticipantId] = [Fold].[HouseParticipantId]) - [dbo].[fnHexToNumber]([C].[RunningWinLoss]) AS [HouseStakeAfterRound]
FROM
[dbo].[Round_Complete] AS [C]
INNER JOIN
[dbo].[Fold_Complete] AS [Fold] ON [Fold].[Id] = [C].[Id]
INNER JOIN
[dbo].[Participant_Complete] AS [Participant] ON [Participant].[ParticipantId] = [Fold].[PlayerParticipantId]
This works, but as you can see it will do two trips to database for same nested select. How can I make this only one round trip?

Answer 1

You are referring to the subqueries. That is not a "round trip to the database", which usually refers to an application calling a query.
All the square braces make the query hard to read, but you can fix this using apply:
SELECT [dbo].[fnHexToNumber](p.[Stake]) AS PlayerStake,
h.HouseStake,
([dbo].[fnHexToNumber](p.[Stake]) + [dbo].[fnHexToNumber]([C].RunningWinLoss)) AS PlayerStakeAfterRound,
(h.HouseStake - [dbo].fnHexToNumber(C.RunningWinLoss)) AS HouseStakeAfterRound
FROM [dbo].[Round_Complete] c JOIN
[dbo].[Fold_Complete] f
ON f.[Id] = c.[Id] JOIN
[dbo].[Participant_Complete] pc
ON px.[ParticipantId] = f.[PlayerParticipantId] OUTER APPLY
(SELECT [dbo].[fnHexToNumber]([Stake]) as HouseStake
FROM [dbo].[Participant_Complete] pch
WHERE pch.ParticipantId = f.HouseParticipantId
) h

Answer 2

Just join the same table a second time instead of pulling the data as sub-queries.
Also, you only need brackets around names if the names contain a space (which is bad practice in general). If the names don't have a space, the brackets are totally extraneous.
SELECT
dbo.fnHexToNumber(Participant.Stake) AS PlayerStake,
dbo.fnHexToNumber(p.Stake) as HouseStake,
(dbo.fnHexToNumber(Participant.Stake) + dbo.fnHexToNumber(C.RunningWinLoss)) AS PlayerStakeAfterRound,
dbo.fnHexToNumber(p.Stake) - dbo.fnHexToNumber(c.RunningWinLoss) as HouseStakeAfterRound
FROM dbo.Round_Complete AS C
INNER JOIN dbo.Fold_Complete AS Fold
ON Fold.Id = C.Id
INNER JOIN dbo.Participant_Complete AS Participant
ON Participant.ParticipantId = Fold.PlayerParticipantId
INNER JOIN dbo.Participant_Complete AS p
ON p.ParticipantId = Fold.HouseParticipantId