SQL Query to Join Two Tables Based On Closest Timestamp - sql

Question

I need to retrieve the records from dbo.transaction (transaction of all users-more than one transaction for each user) that having timestamp which is closest to the time in dbo.bal (current balance details of each user-only one record for each user)
ie, the resultant records should equal to the no of records in the dbo.bal
Here i tried the below query, am getting only the records less than the time in dbo.bal. But there are some record having timestamp greater than and closest to dbo.bal.time
SELECT dbo.bal.uid,
dbo.bal.userId,
dbo.bal.balance,
dbo.bal.time,
(SELECT TOP 1 transactionBal
FROM dbo.transaction
WHERE TIMESTAMP <= dbo.bal.time
ORDER BY TIMESTAMP DESC) AS newBal
FROM dbo.bal
WHERE dbo.bal.time IS NOT NULL
ORDER BY dbo.bal.time DESC
here is my table structure,
dbo.transaction
---------------
| uid| userId | description| timestamp | credit | transactionBal
-------------------------------------------------------------------------
| 1 | 101 | buy credit1| 2012-01-25 03:23:31.624 | 100 | 500
| 2 | 102 | buy credit5| 2012-01-18 03:13:12.657 | 500 | 700
| 3 | 103 | buy credit3| 2012-01-15 02:16:34.667 | 300 | 300
| 4 | 101 | buy credit2| 2012-01-13 05:34:45.637 | 200 | 300
| 5 | 101 | buy credit1| 2012-01-12 07:45:21.457 | 100 | 100
| 6 | 102 | buy credit2| 2012-01-01 08:18:34.677 | 200 | 200
dbo.bal
-------
| uid| userId | balance | time |
-----------------------------------------------------
| 1 | 101 | 500 | 2012-01-13 05:34:45.645 |
| 2 | 102 | 700 | 2012-01-01 08:18:34.685 |
| 3 | 103 | 300 | 2012-01-15 02:16:34.672 |
And the result should be like,
| Id | userId | balance | time | credit | transactionBal
-----------------------------------------------------------------------------
| 1 | 101 | 500 | 2012-01-13 05:34:45.645 | 200 | 300
| 2 | 102 | 700 | 2012-01-01 08:18:34.685 | 200 | 200
| 3 | 103 | 300 | 2012-01-15 02:16:34.672 | 300 | 300
Please help me.. Any help is must appreciated...Thankyou

Answer 1

It would be helpful if you posted your table structures, but ...
I think your inner query needs a join condition. (That is not actually in your question)
Your ORDER BY clause in the inner query could be ABS(TIMESTAMP - DB0.BAL.TIME). That should give you the smallest difference between the 2.
Does that help ?
Based on the follwing Sql Fiddle http://sqlfiddle.com/#!3/7a900/15 I came up with ...
SELECT
bal.uid,
bal.userId,
bal.balance,
bal.time,
trn.timestamp,
trn.description,
datediff(ms, bal.time, trn.timestamp)
FROM
money_balances bal
JOIN money_transaction trn on
trn.userid = bal.userid and
trn.uid =
(
select top 1 uid
from money_transaction trn2
where trn2.userid = trn.userid
order by abs(datediff(ms, bal.time, trn2.timestamp))
)
WHERE
bal.time IS NOT NULL
ORDER BY
bal.time DESC
I cannot vouch for its performance because I know nothing of your data, but I believe it works.
I have simplified my answer - I believe what you need is
SELECT
bal.uid as baluid,
(
select top 1 uid
from money_transaction trn2
where trn2.userid = bal.userid
order by abs(datediff(ms, bal.time, trn2.timestamp))
) as tranuid
FROM
money_balances bal
and from that you can derive all the datasets you need.
for example :
with matched_credits as
(
SELECT
bal.uid as baluid,
(
select top 1 uid
from money_transaction trn2
where trn2.userid = bal.userid
order by abs(datediff(ms, bal.time, trn2.timestamp))
) as tranuid
FROM
money_balances bal
)
select
*
from
matched_credits mc
join money_balances mb on
mb.uid = mc.baluid
join money_transaction trn on
trn.uid = mc.tranuid

Answer 2

Try:
SELECT dbo.bal.uid,
dbo.bal.userId,
dbo.bal.balance,
dbo.bal.time,
(SELECT TOP 1 transactionBal
FROM dbo.transaction
ORDER BY abs(datediff(ms, dbo.bal.time, TIMESTAMP))) AS newBal
FROM dbo.bal
WHERE dbo.bal.time IS NOT NULL
ORDER BY dbo.bal.time DESC