How decrease logical reads while getting result from view? - sql-server

Question

I have a view which I will mention its code below, when I filter entire code, I get proper logical reads, but when I filter the view, logical reads increases so much!
I used subquery instead of cte, I made so many changes in my code, but I couldn't get proper result
This is my view code:
create view att.view_notRule
as
with timeline
as
(
select person,location,dateTime,d_base
from att.view_pD1
union all
select person,location,dateTime_in,d_base
from att.view_rule
union all
select person,location,dateTime_out,d_base
from att.view_rule
),
timelineRanking
as
(
select person,location,row_number() over (partition by person,location,d_base order by dateTime) rank,dateTime,d_base
from timeline
)
select x.person,x.location,x.dateTime dateTime_start,y.dateTime dateTime_end,x.d_base
from timelineRanking x
inner join timelineRanking y on x.person=y.person and x.location=y.location and x.d_base=y.d_base
where x.rank+1=y.rank and x.rank%2=1
when I execute this query I face so many logical reads:
select *
from att.view_notRule
where person='B18FE132-2779-4E0D-A776-4BD27E7EEB7C'
But, when I filter person, inside the code, I get proper logical reads
I need to execute this:
select *
from att.view_notRule
where person='B18FE132-2779-4E0D-A776-4BD27E7EEB7C'
But getting proper logical reads

Answer 1

When you are querying from a view that can't propagate predicates down to the base tables (which sometimes is due to the view design, and sometimes due to limitations in the query optimizer), a useful pattern is to replace the view with a In-Line Table-Valued Function, which is kind of like a parameterized view.
eg:
create or alter function att.view_notRule(#person varchar(200)) returns table
as return
with timeline
as
(
select person,location,dateTime,d_base
from att.view_pD1
where person = #person
union all
select person,location,dateTime_in,d_base
from att.view_rule
where person = #person
union all
select person,location,dateTime_out,d_base
from att.view_rule
where person = #person
),
timelineRanking
as
(
select person,location,row_number() over (partition by person,location,d_base order by dateTime) rank,dateTime,d_base
from timeline
)
select x.person,x.location,x.dateTime dateTime_start,y.dateTime dateTime_end,x.d_base
from timelineRanking x
inner join timelineRanking y on x.person=y.person and x.location=y.location and x.d_base=y.d_base
where x.rank+1=y.rank and x.rank%2=1
Then if you need to run the view across multiple people, you can do so with CROSS APPLY. But for your

Answer 2

If the logical reads is the concern i would normally start to filter base tables (as mentioned by David Browne). In your case, it would go as function instead of view by applying WHERE clause inside CTE.
Also, I would suggest to avoid self join instead use LEAD() function, following is the same example that you can start with:
Declare #PersonID varchar(20) = 'YourData';
with timeline
as
(
select person, location, dateTime, d_base
from att.view_pD1
where person = #PersonID
union all
select person, location, dateTime_in, d_base
from att.view_rule
where person = #PersonID
union all
select person, location, dateTime_out, d_base
from att.view_rule
where person = #PersonID
)
select person,
location,
d_base,
dateTime as StartTime,
LEAD(dateTime) over (partition by person, location, d_base order by dateTime) EndTime
from timeline
go
or To get extreme start and end date, you may start with following:
Declare #PersonID varchar(20) = 'YourData';
select m.person,
m.location,
m.d_base,
s.datetime as StartTime,
e.datetime as EndTime
from att.<viewMasterData> as M
LEFT JOIN
(select person, location, datetime, d_base,
ROW_NUMBER () OVER (Partition by person, location, d_base order by datetime) as StartRN
from att.view_rule
where person = #PersonID
) as s ON M.person = s.person and m.location = s.location and m.base = s.base
LEFT JOIN
(select person, location, datetime, d_base,
ROW_NUMBER () OVER (Partition by person, location, d_base order by datetime desc) as EndRN
from att.view_rule
where person = #PersonID
) as e ON M.person = e.person and m.location = e.location and m.base = e.base
where s.StartRN = 1 and e.EndRN = 1