Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people, just like you, are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
Solved

UPDATE Row using values from prior row

Posted on 2008-09-30
9
736 Views
Last Modified: 2012-05-05
Hello,
I have this:

UPDATE MONEY SET Balance = Credit - Debit + "X"

Ok, that "X" is supposed to be the prior row. I need to calculate the Balance, which is the result of the previous balance + the result of credit + debit. The thing is by the nature of our business we need to alter some old rows and recalculate the balance. The update works that way? How to get the value for a column in the previous row?

thanks.
0
Comment
Question by:starusa
  • 4
  • 3
9 Comments
 
LVL 59

Accepted Solution

by:
Kevin Cross earned 250 total points
ID: 22610200
Do you have an incrementing primary key (PK) or some other column that indicates a row is older than the one you are on?  If so, you could do something like this:


UPDATE MONEY 
SET Balance = Credit - Debit + 
IsNull((SELECT b.balance FROM MONEY b WHERE b.pkColumn IN (SELECT max(pkColumn) FROM MONEY c WHERE c.pkColumn < MONEY.pkColumn)), 0.00)

Open in new window

0
 
LVL 39

Assisted Solution

by:BrandonGalderisi
BrandonGalderisi earned 250 total points
ID: 22610767
I would POSSIBLY suggest not storing the balance then, if values are subject to change.  But that can be figured out

Or, you will have to run this frequently:

;with CurrentPast as
(select AccountNo, TransDate, Credit, Debit, cast(Null as money) as PreviousCredit, cast(Null as money) as PreviousDebit, row_number() over (partition by AccountNo order by TransDate) rn
from Money
union all
select mpAccountNo, mp.TransDate, mp.Credit, mp.Debit, row_number() over (partition by AccountNo order by TransDate) rn
from Money m
join CurrentPast cp
on m.accountNo = cp.AccountNo
and m.rn-1 = cp.rn)
select * from CurrentPast


^^ This will give you the each transaction as pairs. ^^


;with CurrentPast as
(select AccountNo, TransDate, Credit, Debit, cast(credit-debit as money) as CurrentChange, cast(0 as money) as PreviousBalance, row_number() over (partition by AccountNo order by TransDate) rn
from Money
union all
select mp.AccountNo, mp.TransDate, mp.Credit, mp.Debit, row_number() over (partition by AccountNo order by TransDate) rn
from Money m
join CurrentPast cp
on m.accountNo = cp.AccountNo
and m.rn-1 = cp.rn)



Now this is some sample code that shows you how to show a Running balance without ever changing it.  And it allows you to see a balance as of a point in time:



set nocount on
create table #tabMoney
(accountNo     int
,transDate     datetime
,Credit        money
,Debit         money
)
insert into #TabMoney values(1,'1/1/2007',0,20)
insert into #TabMoney values(1,'1/2/2007',20,0)
insert into #TabMoney values(1,'1/3/2007',0,15)
insert into #TabMoney values(1,'1/4/2007',10,0)
 
insert into #TabMoney values(2,'1/1/2007',0,100)
insert into #TabMoney values(2,'2/2/2007',0,50)
insert into #TabMoney values(2,'3/3/2007',160,0)
insert into #TabMoney values(2,'4/1/2007',0,10)
go
;with CurrentPast as
(
select t.* from 
(select AccountNo
     ,TransDate
     ,Credit
     ,Debit
     ,credit-debit as CurrentChange
     ,credit-debit as CurrentBalance
     ,row_number() over (partition by AccountNo order by TransDate) as rn
from #tabMoney) t
where t.rn=1
union all
select m.AccountNo, m.TransDate, m.Credit, m.Debit, m.CreditDebit, cp.CurrentChange+CreditDebit, m.rn
from 
     (select AccountNo
          ,TransDate
          ,Credit
          ,Debit
          ,credit-debit CreditDebit
          ,row_number() over (partition by AccountNo order by TransDate) rn
     from #tabMoney) m
  inner join CurrentPast cp
    on  m.accountNo = cp.AccountNo
    and m.rn-1 = cp.rn
)
select * from CurrentPast
Order by AccountNo,rn
go
drop table #tabMoney

Open in new window

0
 
LVL 39

Expert Comment

by:BrandonGalderisi
ID: 22610769
There are some assumptions based upon field names and structures.  But it can be easily adapted if you table structure is nothing like this.
0
Back Up Your Microsoft Windows Server®

Back up all your Microsoft Windows Server – on-premises, in remote locations, in private and hybrid clouds. Your entire Windows Server will be backed up in one easy step with patented, block-level disk imaging. We achieve RTOs (recovery time objectives) as low as 15 seconds.

 
LVL 59

Expert Comment

by:Kevin Cross
ID: 22610891
I would agree with Brandon on not storing if you don't have to and if you want to use a common table expression and do have SQL 2005 you can modify the first query I gave you to do this:
WITH moneyCTE AS (
    SELECT *,
    row_number() over (ORDER BY transdate) AS rn
    FROM Money
)
UPDATE a
SET a.Balance = a.Credit - a.Debit + IsNull(b.balance, 0.00)
FROM moneyCTE a LEFT JOIN moneyCTE b
ON a.rn-1 = b.rn

Open in new window

0
 
LVL 59

Expert Comment

by:Kevin Cross
ID: 22610901
As Brandon, is saying here is he same query as a select instead of an update.
WITH moneyCTE AS (
    SELECT *,
    row_number() over (ORDER BY transdate) AS rn
    FROM Money
)
SELECT *, -- you can list out columns here
(a.Credit - a.Debit + IsNull(b.balance, 0.00)) AS newBalance
FROM moneyCTE a LEFT JOIN moneyCTE b
ON a.rn-1 = b.rn

Open in new window

0
 
LVL 39

Expert Comment

by:BrandonGalderisi
ID: 22610909
Same basic principal except I contained all of logic within the CTE to simplify the select.  6 & 1/2 dozen :)
0
 
LVL 59

Expert Comment

by:Kevin Cross
ID: 22610948
True.  Was just extending my query and at first glance your query looked much different with the union all statement, but I see now where you were going with that.

Regards,
Kev
0

Featured Post

Free learning courses: Active Directory Deep Dive

Get a firm grasp on your IT environment when you learn Active Directory best practices with Veeam! Watch all, or choose any amount, of this three-part webinar series to improve your skills. From the basics to virtualization and backup, we got you covered.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
TSQL query to generate xml 4 46
Query group by data in SQL Server - cursor? 3 47
MS SQL Server time between records 14 46
SQL Syntax 24 45
Confronted with some SQL you don't know can be a daunting task. It can be even more daunting if that SQL carries some of the old secret codes used in the Ye Olde query syntax, such as: (+)     as used in Oracle;     *=     =*    as used in Sybase …
Composite queries are used to retrieve the results from joining multiple queries after applying any filters. UNION, INTERSECT, MINUS, and UNION ALL are some of the operators used to get certain desired results.​
In an interesting question (https://www.experts-exchange.com/questions/29008360/) here at Experts Exchange, a member asked how to split a single image into multiple images. The primary usage for this is to place many photographs on a flatbed scanner…

856 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question