FInding differences is successive rows in a table

Question

Hi ,
I have a few Audit tables which store all the changes in Entities in my application.. so I have tables like
aud_table1, aud_table2 ...etc ... which have variable structure depending on actual entity audited.
Above table store the complete entity snapshot from original table as soon as they are updated. Now I need to create a difference view where I will compare adjacent rows to find out the difference and display to user. Is it possible to find these differences directly using Sql query may be using Pivot(Crosstabulation)

Answer 1

Hi,
It would by much more efficient to just make one pass through the table, like this:
WITH  cntr     AS
     SELECT     CASE     LEVEL
               WHEN  1  THEN  'Name'
               WHEN  2  THEN  'Quantity'
               WHEN  3      THEN  'Alias'
          END     AS fieldname
     FROM     dual
     CONNECT BY     LEVEL <= 3
,     unpivoted_data     AS
     SELECT     a.entityid
     ,     c.fieldname
     ,     CASE     c.fieldname
               WHEN  'Name'      THEN  a.name
               WHEN  'Quantity'  THEN  TO_CHAR (a.quantity)
               WHEN  'Alias'       THEN  a.alias
          END     AS newvalue
     ,      a.updatedby
     ,     a.updatedon
     FROM          auit_table     a
     CROSS JOIN     cntr          c
,     got_oldvalue     AS
     SELECT     u.*
     ,     LAG (newvalue, 1, newvalue) OVER ( PARTITION BY  entity_id
                                                  ,                fieldname
                                 ORDER BY      updatedon
                               ) AS oldvalue
     FROM     unpivoted_data     u
SELECT    entitiyid
,       fieldname
,       oldvalue
,       newvalue
,       updatedby
,       updatedon
FROM       got_oldvalue
WHERE       LNNVL (oldvalue = newvalue)
ORDER BY  entityid
,            updatedon
,       fieldname
;If you would post CREATE TABLE and INSERT statements for your sample data, then I could test this.
Edited by: Frank Kulash on May 18, 2010 11:59 PM
Tested