How to find max value in SQL Server 2014? - sql

Question

I have a table named StatementSummary.
SELECT *
FROM StatementSummary
WHERE AccountID = 1234
Results
StatementId StatementDate AccountId AmountDue
-------------------------------------------------
100 2017-10-16 1234 600
99 2017-09-16 1234 500
98 2017-08-16 1234 400
I have another table that has a list of Accounts. I am trying to give results that show the last AmountDue for each account
My code:
SELECT
AccountID,
(SELECT MAX(StatementDate)
FROM StatementSummary
GROUP BY AccountID) LastStatementDate,
AmountDue
FROM
Accounts A
INNER JOIN
StatementSummary S ON A.AccountId = S.AccountId
Basically, I want to show all the details of the last statement for every AccountId.

Answer 1

You can use the SQL Server Windowing functions in cases like this.
SELECT DISTINCT
a.AccountId,
FIRST_VALUE(s.StatementDate) OVER (PARTITION BY s.AccountId ORDER BY s.StatementDate DESC) As LastStatementDate,
FIRST_VALUE(s.AmountDue) OVER (PARTITION BY s.AccountId ORDER BY s.StatementDate DESC) As LastAmountDue
FROM Accounts a
INNER JOIN StatementSummary s
ON a.AccountId = s.AccountId
Basically what happens is the OVER clause creates partitons in your data, in this case, by the account number (these partitions are the windows). We then tell SQL Server to sort the data within each partition by the statement date in descending order, so the last statement will be at the top of the partition, and then the FIRST_VALUE function is used to just grab the first row.
Finally, since you perform this operation for every account/statement combo between the two tables, you need the DISTINCT to say you just want one copy of each row for each account.
There are quite a bit of useful things you can do with the windowing functions in SQL Server. This article gives a good introduction to them: https://www.red-gate.com/simple-talk/sql/learn-sql-server/window-functions-in-sql-server/

Answer 2

Derived Table over row numberand left join - to display all accounts regardless if there is a statement
select *
from
(select row_number() over (partition by accountid order by statementdate desc) rn,
accountid, statementdate,amount
from statementtable
) l
left outer join accountstable a
on l.accountid = a.accountid
And l.rn = 1

Answer 3

That's sounds like a job for me sings lateral join aka cross apply in T-SQL.
SELECT a.*, last_ss.*
FROM Accounts A
cross apply (
select top 1 *
from StatementSummary S ON A.AccountId = S.AccountId
order by StatementDate desc
) last_ss
Alternatively you can use CTE to get last date for account:
; with l as (
select accountid, max(StatementDate)
from StatementSummary
group by accountid
)
select ...
from Accounts a
inner join l on l.accountid = a.accountid
inner join StatementSummary ss on ss.accountid = a.accountid
and l.StatementDate = ss.StatementDate