Displaying the difference between rows in the same table in SQL SERVER - sql

Question

I'm using SQL Server 2005.
I have a table that has an archive of rows each time some field was changed. I have to produce a report that displays fields that were changed for each employee.
My table schema:
tblEmp(empid, name, salary, createddate)
My table data:
Row 1: 1, peter, 1000, 11/4/2012
Row 2: 1, peter, 2000, 11/5/2012
Row 3: 1, pete, 2000, 11/6/2012
Row 4: 1, peter, 4000, 11/7/2012
Based on the above data for employee Peter (employee id 1), the output (changes) would be:
resultset:
1, oldsalary: 1000 newsalary: 2000 (changed on 11/5/2012)
1, oldname: peter newname: pete (changed on 11/6/2012)
1, oldname: pete newname: peter, oldsalary:2000, newsalary: 4000 (changed on 11/7/2012)
I'm trying to come up with the sql that would produce the above resultset.
I've tried to do something similar to the first answer in this thread: How to get difference between two rows for a column field?
However, it's not coming together, so wondering if anyone could help.

Answer 1

You are looking at the difference column by column. This suggests using unpivot. The following creates output with each change in a column, along with the previous value and date:
DECLARE #t TABLE(empid INT,name SYSNAME,salary INT,createddate DATE);
INSERT #t SELECT 1, 'peter', 1000, '20121104'
UNION ALL SELECT 1, 'peter', 2000, '20121105'
UNION ALL SELECT 1, 'pete', 2000, '20121106'
UNION ALL SELECT 1, 'peter', 4000, '20121107';
with cv as (
select empid, createddate, col, val
from (select empid, CAST(name as varchar(8000)) as name,
CAST(salary as varchar(8000)) as salary, createddate
from #t
) t
unpivot (val for col in (name, salary)) as unpvt
),
cvr as (
select cv.*,
ROW_NUMBER() over (partition by empid, col order by createddate) as seqnum_all
from (select cv.*, ROW_NUMBER() over (partition by empid, col, thegroup order by createddate) as seqnum_group
from (select cv.*,
(ROW_NUMBER() over (partition by empid, col order by createddate) -
ROW_NUMBER() over (partition by empid, col, val order by createddate)
) as thegroup
from cv
) cv
) cv
where seqnum_group = 1
) -- select * from cvr
select cvr.*, cvrprev.val as preval, cvrprev.createddate as prevdate
from cvr left outer join
cvr cvrprev
on cvr.empid = cvrprev.empid and
cvr.col = cvrprev.col and
cvr.seqnum_all = cvrprev.seqnum_all + 1

Answer 2

Perhaps these joined CTE's with ROW_NUMBER + CASE:
WITH cte AS
(
SELECT empid,
name,
salary,
rn=ROW_NUMBER()OVER(PARTITION BY empid ORDER BY createddate)
FROM tblemp
)
SELECT oldname=CASE WHEN c1.Name=c2.Name THEN '' ELSE C1.Name END,
newname=CASE WHEN c1.Name=c2.Name THEN '' ELSE C2.Name END,
oldsalary=CASE WHEN c1.salary=c2.salary THEN NULL ELSE C1.salary END,
newsalary=CASE WHEN c1.salary=c2.salary THEN NULL ELSE C2.salary END
FROM cte c1 INNER JOIN cte c2
ON c1.empid=c2.empid AND c2.RN=c1.RN + 1
Sql-Fiddle Demo

Answer 3

DECLARE #t TABLE(empid INT,name SYSNAME,salary INT,createddate DATE);
INSERT #t SELECT 1, 'peter', 1000, '20121104'
UNION ALL SELECT 1, 'peter', 2000, '20121105'
UNION ALL SELECT 1, 'pete', 2000, '20121106'
UNION ALL SELECT 1, 'peter', 4000, '20121107';
;WITH x AS
(
SELECT empid, name, salary, createddate, rn = ROW_NUMBER() OVER
(PARTITION BY empid ORDER BY createddate)
FROM #t
-- WHERE empid = 1 -- for example
)
SELECT LTRIM(
CASE WHEN x.salary <> y.salary THEN
'oldsalary: ' + RTRIM(x.salary)
+ ' newsalary: ' + RTRIM(y.salary)
ELSE '' END
+ CASE WHEN x.name <> y.name THEN
' oldname: ' + x.name
+ ' newname: ' + y.name
ELSE '' END
+ ' (changed on ' + CONVERT(CHAR(10), y.createddate, 101) + ')')
FROM x INNER JOIN x AS y
ON x.rn = y.rn - 1
AND x.empid = y.empid
AND
(
x.salary <> y.salary
OR x.name <> y.name
);
Unless you have a where clause to target a specific empid, however, the output is not very useful unless it also includes empid. SQLfiddle demo

Answer 4

Based on what you explain, It would be easier to create a Trigger when this table is Changed and then create the table with the result you expect, Since you have in that moment the old values and the New values, there should be not a problem to come up with the result you expect.