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

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.

Solution 1

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

Solution 2

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

Solution 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