I think I found some explanations and will answer my own question :

The "declare @p5 unknown" in rpc:completed event was merely a side effect of a timeout. Whenever I set an very high time out, the query will complete (sometimes in 20 minutes) and the rpc:completed event will display "declare @p5 dbo.TypeTableGuid" indeed.

I've been fooled by several different intefering problem in fact : The query was made of a lot of

• insert into @p5 values('XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX')

before a (this is an oversimplified example but the actual query does start with "SELECT TOP(1)")

• exec sp_executesql N'SELECT TOP(1) from table1 inner join @Listeguid L on L.Value = table1.id',N'@Listeguid [dbo].[TypeTableGuid] READONLY', @Listeguid =@p5

The number of insert varied from 10000 to 65000 as I realised later by debugging the application code. But I suspect the profiler can only save so many characters per query, which would explain why it never recorded more than

• the first 6521 inserts,
• and then the actual query (SELECT TOP(1) ...) at the very end

in the trace.

The copy/Paste from the profiler to SSMS was then a useless test : the result was always the one I expected (SELECT TOP(1) ...), but based on a subset of data (6521 guid) instead of 65000, so the performance from SSMS were always good.

I can now work on something a bit more interesting, like why this query goes off the rails from time to time or if there is a better way to formulate it. I'm not sure that that udtt variable holding 65000 guid values is a good option...