How can I modify one column of current and next record depending of some criteria?

Question

Having DDL
CREATE TABLE #ServiceChange(
[ID] [int] identity(1,1),
[SHCOMP] [char](2) NOT NULL,
[SHCRTD] [numeric](8, 0) NOT NULL,
[SHCUST] [numeric](7, 0) NOT NULL,
[SHDESC] [char](35) NOT NULL,
[SHTYPE] [char](1) NOT NULL,
[SHAMT] [numeric](9, 2) NOT NULL,
[CBLNAM] [char](30) NOT NULL,
[GROUPID] [char](2) NULL
And original and desire data in below link
https://www.dropbox.com/sh/bpapxquaae9aa13/AADnan31ZASublDjN7sa2Vvza
I would like to know how can I modify one column of current and next record depending of some criteria using SQL2012?
The criteria is:
Type should always flow F->T
if current abs(amount)> next abs(amount) then groupid = 'PD'
if current abs(amount)< next abs(amount) then groupid = 'PI'
there is no case when those amounts will be equals
where current(custid) = next(custid) and current(service) = next(service) and groupid is null
Any help will be really apreciated.
Thank you

Answer 1

I tried that and got this error
'LAG' is not a recognized built-in function name.
You said you were using SQL 2012, but apparently you are not. The LAG function was added in SQL 2012. This solution works on SQL 2005 and SQL 2008:
; WITH numbering AS (
   SELECT groupid,
          rowno = row_number()  OVER (PARTITION BY custid, service ORDER BY date, id)
   FROM   #ServiceChange
), CTE AS (
   SELECT a.groupid,
          CASE WHEN abs(a.amount) < abs(b.amount) THEN 'PD'
               WHEN abs(a.amount) > abs(b.amount) THEN 'PI'
          END AS newgroupid
   FROM  numbering a
   JOIN  numbering b ON b.custid  = a.custid
                    AND b.service = a.service
                    AND b.rowno   = a.rowno - 1
UPDATE CTE
SET   groupid = newgroupid
Erland Sommarskog, SQL Server MVP, [email protected]