USQL nested query performance - query-performance

Question

I have a USQL query that runs fine on it's own against 400M records in a managed table.
But during development, I don't want to run it against all records all the time, so I pop a where clause in, run it for a tiny subsection of data, and it completes in around 2 minutes (#5 AUs), writing out results to a tsv in my data lake.
Happy with that.
However, I now want to use it as the source for a second query and further processing.
So I create a view with the original USQL (minus the where clause).
Then to test, a new script :
'Select * from MyView WHERE <my original test filter>'.
Now I was expecting that to execute in around the same time as the original raw query. But instead I got to 4 minutes, only 10% through the plan, and cancelled - something is not right.
No expert at reading Job Graphs, but ...
The original script kicks off with 2* 'Extract Combine partition' both reading a couple of hundered MBs, my select on the saved View is reading over 100GB !!
So it is not taking the where clause into account at all at this stage.
Obviously this shows how little I yet understand about how DLA works behind the scenes !
Would someone please help me understand (a) what is going on and (b) a path forward to get the behavior I need ?
Currently having a play with stored procedures to store the 1st result in a table and then call the second query against that - but just seems overkill compared with 'traditional' SQL Server ?!?
All pointers & hints appreciated !
Many Thanks
Original Base Query:
CREATE VIEW IF NOT EXISTS Play.[M3_CycleStartPoints]
AS
//#BASE =
SELECT ROW_NUMBER() OVER (PARTITION BY A.[CTNNumber] ORDER BY A.[SeqNo]) AS [CTNCycleNo], A.[CTNNumber], A.[SeqNo], A.[BizstepDescription], A.[ContainerStatus], A.[FillStatus]
FROM
[Play].[RawData] AS A
LEFT OUTER JOIN
(
SELECT [CTNNumber],[SeqNo]+1 AS [SeqNo],[FillStatus],[ContainerStatus],[BizstepDescription]
FROM [Play].[RawData]
WHERE [FillStatus] == "EMPTY" AND [AssetUsage] == "CYLINDER"
) AS B
ON A.[CTNNumber] == B.[CTNNumber] AND A.[SeqNo] == B.[SeqNo]
WHERE (
(A.[FillStatus] == "FULL" AND
A.[AssetUsage] == "CYLINDER" AND
B.[CTNNumber] == A.[CTNNumber]
) OR (
A.[SeqNo] == 1
)
);
//AND A.[CTNNumber] == "BE52XH7";
//Only used to test when running script as stand-alone & output to tsv
Second Query
SELECT *
FROM [Play].[M3_CycleStartPoints]
WHERE [CTNNumber] == "BE52XH7";

Answer 1

Ok, I think I've got this, or at least in part.
Table valued Functions
http://www.sqlservercentral.com/articles/U-SQL/146839/
to allow the passing of an argument to a view and return the result.
Would be interested in finding some reading material around this subject still though.
Coming from a T-SQL world, seems that there are some fundamental differences I'm still tripping over.