CROSS APPLY with table valued function restriction performance
I have problem with CROSS APPLY
with parametrised table valued function. Here is simplified pseudo code example:
SELECT *
FROM (
SELECT lor.*
FROM LOT_OF_ROWS_TABLE lor
WHERE ...
) AS lor
CROSS APPLY dbo.HeavyTableValuedFunction(lor.ID) AS htvf
INNER JOIN ANOTHER_TABLE AS at ON lor.ID = at.ID
WHERE ...
LOT_OF_ROWS_TABLE
is returning many rows. LOT_OF_ROWS_TABLE
and ANOTHER_TABLE
returns only one or few rows. My problem:
The function is called for all rows returned from LOT_OF_ROWS_TABLE
regardless of the fact that the data will be limited when just join ANOTHER_TABLE
.
The select has to be in the shown format - it is generated and in fact it is much more dificult.
When I try to rewrite it, it can be very fast, but it cannot be rewritten like this:
SELECT *
FROM (
SELECT lor.*
FROM LOT_OF_ROWS_TABLE lor
WHERE ...
) AS lor
INNER JOIN ANOTHER_TABLE AS at ON lor.ID = at.ID
CROSS APPLY dbo.HeavyTableValuedFunction(at.ID) AS htvf
WHERE ...
I'd like to know:
Is there any setting or hint or something that forces select to call function only for finally restricted rows?
Thank you.
EDIT:
The table valued function is very complex: http://pastebin.com/w6azRvxR. The select we are talking about is "user configured" and generated: http://pastebin.com/bFbanY2n.
you can divide this query into 2 parts use either table variable or temp table
SELECT lor.*,at.* into #tempresult
FROM (
SELECT lor.*
FROM LOT_OF_ROWS_TABLE lor
WHERE ...
) lor
INNER JOIN ANOTHER_TABLE AS at ON lor.ID = at.ID
WHERE ...
now do the time consuming part which is table valued function right
SELECT * FROM #tempresult
CROSS APPLY dbo.HeavyTableValuedFunction(#tempresult.ID) AS htvf
I believe this is what you are looking for.
Plan Forcing Scenario: Create a Plan Guide to Force a Plan Obtained from a Rewritten Query
Basically it describes re-writing the query to get a generated plan using the correct order of joins. Then saving off that plan and forcing your existing query (that does not get changed) to use the plan you saved off.
The BOL link I put in even gives a specific example of re-writing the query putting the joins in a different order and using a FORCE ORDER
hint. Then using sp_create_plan_guild
to take the plan from the re-written query and use it on the original query.
YES and NO... it's hard to interprit what you're trying to achieve without sample data IN and result OUT, to compare outcomes.
I'd like to know:
Is there any setting or hint or something that forces select to call function only for finally restricted rows?
So I'll answer your question above (3 years later!!) directly, with a direct statement:
You need to learn about CTE and the difference between CROSS APPLY compared to INNER JOIN and why using CROSS APPLY in your case is necessary. You "could" take the code in your function and apply it into a single SQL statement using CTE.
ie:
Read this and this.
Essentially, something like this...
WITH t2o AS
(
SELECT t2.*, ROW_NUMBER() OVER (PARTITION BY t1_id ORDER BY rank) AS rn
FROM t2
)
SELECT t1.*, t2o.*
FROM t1
INNER JOIN
t2o
ON t2o.t1_id = t1.id
AND t2o.rn <= 3
Apply your query to extrapolate the date you want ONCE, and using CTE, then apply your second SQL using the CROSS APPLY.
You have no choice. You cannot do what you're trying to do in ONE SQL.
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