Concurrent create or select statement failing with deadlock error - sql-server

Question

Where running the following SQL statement currently (maybe 30 or 40 times at the same time) and is giving us deadlock errors but we're not sure which statements are interfering with each other. There are no indexes on the Things table besides a PK and a Fk to ThingTypes table. We're also wondering if adding an index to ThingTypeId and HourId will help resolve the issue. Lastly it's also safe for us to assume that {#thingTypeID and #hourID} are unique for all the concurrent queries and the if is only there for if this was re-run at a later period in time.
Transaction (Process ID 237) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction
Code:
IF NOT EXISTS(select top(1) id from [eddsdbo].[Things] (UPDLOCK)
where [ThingTypeID] = #thingTypeID and [HourID] = #hourID)
BEGIN
INSERT INTO [eddsdbo].[Things]
([ThingTypeID]
,[HourID])
VALUES
(#thingTypeID
,#hourID)
SELECT m.*, mt.SampleType
FROM [eddsdbo].[Things] as m
inner join [eddsdbo].[ThingTypes] as mt on mt.Id = m.ThingTypeID
WHERE m.ID = ##IDENTITY
END
ELSE
BEGIN
SELECT m.*, mt.SampleType
FROM [eddsdbo].[Things] as m
inner join [eddsdbo].[ThingTypes] as mt on mt.Id = m.ThingTypeID
where [ThingTypeID] = #thingTypeID and [HourID] = #hourID
END
We've been chasing down this issue for a while so any help is appreciated.

Answer 1

Not sure this will fix it
But do you you really need the WHERE m.ID = ##IDENTITY
IF NOT EXISTS(select top(1) id from [eddsdbo].[Things] (UPDLOCK)
where [ThingTypeID] = #thingTypeID and [HourID] = #hourID)
BEGIN
INSERT INTO [eddsdbo].[Things]
([ThingTypeID], [HourID])
VALUES (#thingTypeID, #hourID)
END
SELECT m.*, mt.SampleType
FROM [eddsdbo].[Things] as m
inner join [eddsdbo].[ThingTypes] as mt
on mt.Id = m.ThingTypeID
and [ThingTypeID] = #thingTypeID
and [HourID] = #hourID
A single statement is a transaction
I think this will have less overhead
DECLARE #t AS TABLE (id int identity primary key, thingTypeID int, hourID int);
declare #thingTypeID int = 1, #hourID int = 2;
insert into #t (thingTypeID, hourID)
values (#thingTypeID, #hourID);
select *
from #T
where thingTypeID = #thingTypeID and hourID = #hourID;
insert into #t (thingTypeID, hourID)
select #thingTypeID, #hourID
where not exists (select 1 from #t where thingTypeID = #thingTypeID and hourID = #hourID);
select *
from #T
where thingTypeID = #thingTypeID and hourID = #hourID;
set #thingTypeID = 1;
set #hourID = 3;
insert into #t (thingTypeID, hourID)
select #thingTypeID, #hourID
where not exists (select 1 from #t where thingTypeID = #thingTypeID and hourID = #hourID);
select *
from #T
where thingTypeID = #thingTypeID and hourID = #hourID;
select *
from #T
order by id;