SQL Query + more efficient alternative - sql

Question

I have a query which involves 2 tables 'Coupons' and 'CouponUsedLog' in SQL Server, the query below will obtain some information from these 2 tables for statistics study use. Somehow I feel that while my query works and returns me the desired results, I feel that I can be written in a more efficient way, can someone please advice if there's a better way to rewrite this? Am I using too many unnecessary variables and joins? Thanks.
DECLARE #CouponISSUED int=null
DECLARE #CouponUSED int=null
DECLARE #CouponAVAILABLE int=null
DECLARE #CouponEXPIRED int=null
DECLARE #CouponLastUsed Date=null
--Total CouponIssued
SET #CouponISSUED =
(
select count(*)
from Coupon C Left Join
couponusedlog CU on C.autoid = CU.Coupon_AutoID
where C.VoidedBy is null and
C.VoidedOn is null and
DeletedBy is null and
DeletedOn is null and
Card_AutoID in (Select AutoID
from Card
where MemberID = 'Mem001')
)
--Total CouponUsed
SET #CouponUSED =
(
select count(*)
from couponusedlog CU Left Join
Coupon C on CU.Coupon_AutoID = V.autoid
where CU.VoidedBy is null and
CU.VoidedOn is null and
C.Card_AutoID in (select AutoID
from Card
where MemberID = 'Mem001')
)
SET #CouponAVAILABLE = #CouponISSUED - #CouponUSED
--Expired Coupons
SET #CouponEXPIRED =
(
select Count(*)
from Coupon C Left Join
couponusedlog CU on C.autoid = CU.Coupon_AutoID
where C.VoidedBy is null and
C.VoidedOn is null and
deletedBy is null and
deletedOn is null and
Card_AutoID in (select AutoID
from Card
where MemberID = 'Mem002') and
CONVERT (date, getdate()) > C.expirydate
)
--Last Used On
SET #CouponLastUsed =
(
select CONVERT(varchar(10),
Max(VU.AddedOn), 103) AS [DD/MM/YYYY]
from couponusedlog CU Left Join
coupon C on CU.Coupon_AutoID = C.autoid
where CU.voidedBy is null and
CU.voidedOn is null and
C.Card_AutoID in (select AutoID
from Card
where MemberID = 'Mem002')
)
Select #CouponISSUED As Coupon_Issued,
#CouponUSED As Coupon_Used,
#CouponAVAILABLE As Coupon_Available,
#CouponEXPIRED As Coupon_Expired,
#CouponLastUsed As Last_Coupon_UsedOn

Answer 1

In general its better to do things in a single query if you you're just looking for counts of things particularly against nearly the same data set then in four separate queries.
This query combines what you need into a single query by converting your WHERE Clauses into SUMS of CASE statements. The MAX of the date is just a normal thing you can do when you're doing a count or a sum.
SELECT COUNT(*) couponissued,
SUM(CASE
WHEN deletedby IS NULL
AND deletedon IS NULL THEN 1
ELSE 0
END) AS couponused,
SUM(CASE
WHEN deletedby IS NULL
AND deletedon IS NULL
AND Getdate() > c.expirydate THEN 1
ELSE 0
END) AS couponex,
MAX(vu.addedon) CouponEXPIRED
FROM [couponusedlog] cu
LEFT JOIN [Coupon] c
ON ( cu.coupon_autoid = v.autoid )
WHERE cu.voidedby IS NULL
AND cu.voidedon IS NULL
AND ( c.card_autoid IN (SELECT [AutoID]
FROM [Card]
WHERE memberid = 'Mem001') )
You can then convert that into a Common Table Expression to do your subtraction and formatting

Answer 2

Are you asking this question out of a proactive desire to be as effecient as possible, or because of an actual performance issue you would like to correct? You can make this more effecient at the cost of having code that is harder to manage. If the performance is okay right now I would highly recommend you leave it because the next person to come along will be able to understand it just fine. If you make one huge effecient but garbled sql statement out of it then when you or anyone else wants to update something about it it's going to take you 3 times longer as you try to re-figure out what the heck you were thinking when you wrote it.