Join max date from a related table - sql

Question

I have the following queries:
select AccountId
into #liveCustomers
from AccountExtensionBase where New_duos_group not in ('T053','T054')
and New_AccountStage = 7
select AccountId
into #customerWhoLeft
from New_marketmessagein as a
inner join AccountExtensionBase as b on a.new_accountmminid = b.AccountId
where New_MessageTypeCode = '105L'
and a.New_EffectiveFromDate > '30 jun 2016'
and b.New_duos_group not in ('T053','T054')
select
accountid
, New_MPRNNumber
, New_duos_group
, New_CommercialAgreementDayRate
, New_CommercialAgreementNightRate
, New_CommercialAgreementHeatRate
, New_Tariffpriceagreedatsignup
, New_Tariffname
into
#monthCustomers
from
AccountExtensionBase
where
AccountId in (select * from #customerWhoLeft)
or
AccountId in (select * from #liveCustomers)
I now wish to join a table called usagefactorExtensionBase and join only the row containing the most recent read date but when I try to join this to my table of 4985 monthly customers I get like 106,813 rows using this code so I think my join or methodology has gone awry, can someone please help me correct the error so I display the list of monthCustomers plus the read details of their most recent read.
Attempting:
select
accountid
, New_MPRNNumber
, New_duos_group
, New_CommercialAgreementDayRate
, New_CommercialAgreementNightRate
, New_CommercialAgreementHeatRate
, New_Tariffpriceagreedatsignup
, New_Tariffname
, max(b.New_EffectiveFromDate)
, b.New_ActualUsageFactor
, b.New_EstimatedUseage
from
#monthCustomers as a
left join
New_marketmessageinusagefactorExtensionBase as b
on a.AccountId = b.new_accountmmusagefactorid
group by
accountid
, New_MPRNNumber
, New_duos_group
, New_CommercialAgreementDayRate
, New_CommercialAgreementNightRate
, New_CommercialAgreementHeatRate
, New_Tariffpriceagreedatsignup
, New_Tariffname
, b.New_ActualUsageFactor
, b.New_EstimatedUseage

Answer 1

try this,
SELECT
accountid,
New_MPRNNumber,
New_duos_group,
New_CommercialAgreementDayRate,
New_CommercialAgreementNightRate,
New_CommercialAgreementHeatRate,
New_Tariffpriceagreedatsignup,
New_Tariffname,
b.New_EffectiveFromDate,
b.New_ActualUsageFactor,
b.New_EstimatedUseage
FROM #monthCustomers AS a
-- Get only max date rows for each AccountID
LEFT JOIN( SELECT t1.*
FROM New_marketmessageinusagefactorExtensionBase AS t1
INNER JOIN ( SELECT new_accountmmusagefactorid, MAX(New_EffectiveFromDate) AS New_EffectiveFromDate_Max
FROM New_marketmessageinusagefactorExtensionBase
GROUP BY new_accountmmusagefactorid
) AS t2 ON t2.new_accountmmusagefactorid = t1.new_accountmmusagefactorid
AND t2.New_EffectiveFromDate_Max = t1.New_EffectiveFromDate
)AS b
ON a.AccountId = b.new_accountmmusagefactorid
there might be rows with same date, try below if is works,
SELECT
accountid,
New_MPRNNumber,
New_duos_group,
New_CommercialAgreementDayRate,
New_CommercialAgreementNightRate,
New_CommercialAgreementHeatRate,
New_Tariffpriceagreedatsignup,
New_Tariffname,
b.New_EffectiveFromDate,
b.New_ActualUsageFactor,
b.New_EstimatedUseage
FROM #monthCustomers AS a
-- Get only max date rows for each AccountID
LEFT JOIN( SELECT New_MPRNNumber,
New_duos_group,
New_CommercialAgreementDayRate,
New_CommercialAgreementNightRate,
New_CommercialAgreementHeatRate,
New_Tariffpriceagreedatsignup,
New_Tariffname,
MAX(New_EffectiveFromDate) AS New_EffectiveFromDate,
New_ActualUsageFactor,
New_EstimatedUseage
FROM New_marketmessageinusagefactorExtensionBase AS t1
GROUP BY
New_MPRNNumber,
New_duos_group,
New_CommercialAgreementDayRate,
New_CommercialAgreementNightRate,
New_CommercialAgreementHeatRate,
New_Tariffpriceagreedatsignup,
New_Tariffname,
New_ActualUsageFactor,
New_EstimatedUseage
)AS b
ON a.AccountId = b.new_accountmmusagefactorid