Get the 1st occurrence of a row based on column value
I already have a query that gets the data I need but it's pretty slow. I'm looking to get this data in the fastest way possible.
Or, to ask another way, given the following simple set of data...
Element_Id Property_Id Value
2528 1 Company conameshort
-4096 1
2528 2 Company Name
-4096 2 Text
-4096 3 Company Text Field
2528 5 6
-4096 5 3
Element_Id Property_Id Value
2528 1 Company conameshort
2528 2 Company Name
-4096 3 Company Text Field
2528 5 6
properties.xlsx
I'm using Microsoft SQL Server 2012
pseudo code:
select element_id, property_id, value
from (
select element_id, property_id, value,
row_number() over(partition by property_id order by property_id, element_id desc) rn
from (
select blah, blah blah from junk1 cross apply junk2
) t2
) t1
where rn=1
Guess a temp table or materialize view from the cross join then using row_number isn't an option either since it uses row_number?
So it would appear that I was operating under a false assumption that ROW_NUMBER() is slow. I had an interesting few hours last weekend figuring out why my view was running so slow. It turned out that my view uses an APPLY clause to call a user defined function. It's the UDF that is using the ROW_NUMBER() function. When using CROSS APPLY, performance of the view is about twice as slow as when using OUTER APPLY. Furthermore, if I filter the view with any kind of WHERE clause, performance of the view drops even further when using CROSS APPLY. My solution was to just use OUTER APPLY for the view and now performance is great. The UDF is still using ROW_NUMBER(). Thanks all for your contributions.
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