Selecting records with maximum value in group - sql

Question

I have a transaction table with the following structure:
select t.[GUID], t.[ID], ts.Description "Status", t.Payee, t.Amount, t.SequenceNumber
from [Transaction] t
inner join TransactionStatus ts on t.StatusID = ts.ID
GUID | ID | Status | Payee | Amount | SequenceNumber
AF732CF5-E6C0-E411-B8F6-004056AB77C2 | 1 | Posted | Amy | 500.00 | 1
AF732CF5-E6C0-E411-B8F6-004056AB77C2 | 2 | Voided | Amy | 500.00 | 2
1F7D880C-E7C0-E411-B8F6-004056AB77C2 | 3 | Posted | Bob | 70.00 | 1
AF732CF5-E6C0-E411-B8F6-004056AB77C2 | 4 | Posted | Amy | 512.50 | 3
1F7D880C-E7C0-E411-B8F6-004056AB77C2 | 5 | Posted | Bob | 66.00 | 2
F2CC0B03-76C7-E411-A48D-004056AB787C | 6 | Pending | Carol | 240.00 | NULL
I'm trying to construct a query to group the records by GUID and select the single record with the largest SequenceNumber (if it isn't NULL):
GUID | ID | Status | Payee | Amount | SequenceNumber
AF732CF5-E6C0-E411-B8F6-004056AB77C2 | 4 | Posted | Amy | 512.50 | 3
1F7D880C-E7C0-E411-B8F6-004056AB77C2 | 5 | Posted | Bob | 66.00 | 2
F2CC0B03-76C7-E411-A48D-004056AB787C | 6 | Pending | Carol | 240.00 | NULL
I've tried adding this line:
where SequenceNumber = (select MAX(SequenceNumber) from [Transaction] t2 where t.[GUID] = t2.[GUID])
but that doesn't get me any transactions where the status is Pending (they don't have sequence numbers). How can I fix this query?

Answer 1

If it's SQL-Server you can use a CTE + ROW_NUMBER:
WITH CTE AS
(
select t.[GUID], t.[ID], ts.Description "Status", t.Payee, t.Amount, t.SequenceNumber,
rn = row_number() over (partition by t.[GUID] Order By t.SequenceNumber DESC)
from [Transaction] t
inner join TransactionStatus ts on t.StatusID = ts.ID
)
SELECT GUID, ID, Status, Payee, Amount, SequenceNumber
FROM CTE
WHERE rn = 1
This will include the row where SequenceNumber is null. If you want all rows with the maximum SequenceNumber(in case of ties) use DENSE_RANK instead of ROW_NUMBER.

Answer 2

You can calculate the MAX(ID) and it's related [GUID] in a subquery and JOIN to it in order to get the desired results:
Sample subquery:
SELECT [GUID] ,
MAX(ID) MaxId
FROM Transaction
GROUP BY [GUID]
Would produce:
GUID MaxId
1F7D880C-E7C0-E411-B8F6-004056AB77C2 5
AF732CF5-E6C0-E411-B8F6-004056AB77C2 4
F2CC0B03-76C7-E411-A48D-004056AB787C 6
Full Demo:
CREATE TABLE #Transaction
(
[GUID] VARCHAR(36) ,
[ID] INT ,
[Status] VARCHAR(7) ,
[Payee] VARCHAR(5) ,
[Amount] INT ,
[SequenceNumber] VARCHAR(4)
);
INSERT INTO #Transaction
( [GUID], [ID], [Status], [Payee], [Amount], [SequenceNumber] )
VALUES ( 'AF732CF5-E6C0-E411-B8F6-004056AB77C2', 1, 'Posted', 'Amy', 500.00,
'1' ),
( 'AF732CF5-E6C0-E411-B8F6-004056AB77C2', 2, 'Voided', 'Amy', 500.00,
'2' ),
( '1F7D880C-E7C0-E411-B8F6-004056AB77C2', 3, 'Posted', 'Bob', 70.00,
'1' ),
( 'AF732CF5-E6C0-E411-B8F6-004056AB77C2', 4, 'Posted', 'Amy', 512.50,
'3' ),
( '1F7D880C-E7C0-E411-B8F6-004056AB77C2', 5, 'Posted', 'Bob', 66.00,
'2' ),
( 'F2CC0B03-76C7-E411-A48D-004056AB787C', 6, 'Pending', 'Carol',
240.00, NULL );
SELECT #Transaction.*
FROM #Transaction
INNER JOIN ( SELECT [GUID] ,
MAX(ID) MaxId
FROM #Transaction
GROUP BY [GUID]
) t ON t.[GUID] = #Transaction.[GUID]
AND t.MaxId = #Transaction.ID
ORDER BY ID

Answer 3

Try this way to get maximum SequenceNumber
CASE WHEN MAX(SequenceNumber IS NULL) = 0 THEN MAX(SequenceNumber) ELSE NULL END AS SequenceNumber

Answer 4

I don't know if SQL Server has windowing functions, so you may be able to do this more cleanly, but here's a vanilla SQL solution:
select highest.[GUID],
highest.[ID],
ts.Description "Status",
highest.Payee,
highest.Amount,
highest.SequenceNumber
from [Transaction] highest
join TransactionStatus ts
on ts.ID = highest.ID
left join [Transaction] higher
on higher.[GUID] = highest.[GUID]
and higher.SequenceNumber > highest.SequenceNumber
where higher.[GUID] is null;

Answer 5

omething like this:
SELECT * FROM
(
select
t.[GUID], t.[ID], ts.Description "Status", t.Payee, t.Amount,
ROW_NUMBER() OVER PARTITION BY (t.[GUID]
ORDER BY t.SequenceNumber DESC) AS rownum
from [Transaction] t
inner join TransactionStatus ts on t.StatusID = ts.ID
)vals where vals.rownum = 1