Horrible sql server performance when capturing result in variable - sql

Question

I'm using SQL Server 2012.
When I run this query...
select
count(*)
from
MembershipStatusHistory msh
join
gym.Account a on msh.AccountID = a.AccountID
join
gym.MembershipType mt on a.MembershipTypeID = mt.MembershipTypeID
join
MemberTypeGroups mtg on mt.MemberTypeGroupID = mtg.MemberTypeGroupID
where
mtg.MemberTypeGroupID IN (1,2)
and msh.NewMembershipStatus = 'Cancelled'
and year(msh.ChangeDate) = year(getdate())
and month(msh.ChangeDate) = month(getdate())
and day(msh.ChangeDate) = day(getdate())
...it returns almost instantly. Great. Now, when I run the same exact query like this:
declare #CancellationsToday int
SET #CancellationsToday = (
select
count(*)
from MembershipStatusHistory msh
join gym.Account a
on msh.AccountID = a.AccountID
join gym.MembershipType mt
on a.MembershipTypeID = mt.MembershipTypeID
join MemberTypeGroups mtg
on mt.MemberTypeGroupID = mtg.MemberTypeGroupID
where mtg.MemberTypeGroupID IN (1,2)
and msh.NewMembershipStatus = 'Cancelled'
and year(msh.ChangeDate) = year(getdate())
and month(msh.ChangeDate) = month(getdate())
and day(msh.ChangeDate) = day(getdate())
)
...it takes 1.5 MINUTES to return. Consistently, every time.
What the **** is going on? I have to use a variable because I need to sum the result later on in my stored proc. I am storing the results of other queries in the same proc and they are fast. I am stumped.
Here is the execution plan from the SLOW query:
And here is the execution plan from the FAST query:
I'll be honest, I don't know what these execution plans mean or what I need to correct.

Answer 1

Very strange but try something like this....
declare #CancellationsToday int;
select #CancellationsToday = count(*)
from MembershipStatusHistory msh
join gym.Account a
on msh.AccountID = a.AccountID
join gym.MembershipType mt
on a.MembershipTypeID = mt.MembershipTypeID
join MemberTypeGroups mtg
on mt.MemberTypeGroupID = mtg.MemberTypeGroupID
where mtg.MemberTypeGroupID IN (1,2)
and msh.NewMembershipStatus = 'Cancelled'
and year(msh.ChangeDate) = year(getdate())
and month(msh.ChangeDate) = month(getdate())
and day(msh.ChangeDate) = day(getdate())

Answer 2

Mmmm strange, try this:
SELECT #CancellationsToday = COUNT(*) FROM ......
Another thing worth to mention is don't use functions in the WHERE clause.
I think you have only the date in msh.ChangeDate, make a variable with today's date like this:
DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))
and use that in the WHERE clause.

Answer 3

You need to look at the execution plans for both queries in SQL Server Management Studio to understand what's going on and why. There may be an index you can add that will fix things, or the plan itself may tell you what's going side-ways and how to fix it. Without that info, it's hard to know what to say here.
As I commented above, adjusting your where clause to get rid of the six function calls and just compare the "date" portion of the database column with a constant variable should help some.
Another minor suggestion would be to be explicit about INNER JOIN if that's what you want... always specify exactly the type of join you want (INNER JOIN, LEFT OUTER JOIN, CROSS JOIN, etc.) instead of just 'join'. It makes things more clear.