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