comparing 2 consecutive rows in a recordset - sql

Question

Currently,I have this objective to meet. I need to query the database for certain results. After done so, I will need to compare the records:
For example: the query return me with 10 rows of records, I then need to compare: row 1 with 2, row 2 with 3, row 3 with 4 ... row 9 with 10.
The final result that I wish to have is 10 or less than 10 rows of records.
I have one approach currently. I do this within a function, hand have the variables call "previous" and "current". In a loop I will always compare previous and current which I populate through the record set using a cursor.
After I got each row of filtered result, I will then input it into a physical temporary table.
After all the results are in this temporary table. I'll do a query on this table and insert the result into a cursor and then returning the cursor.
The problem is: how can I not use a temporary table. I've search through online about using nested tables, but somehow I just could not get it working.
How to replace the temp table with something else? Or is there other approach that I can use to compare the row columns with other rows.
EDIT
So sorry, maybe I am not clear with my question. Here is a sample of the result that I am trying to achieve.
TABLE X
Column A B C D
100 300 99 T1
100 300 98 T2
100 300 97 T3
100 100 97 T4
100 300 97 T5
101 11 11 T6
ColumnA is the primary key of the table. ColumnA has duplicates because table X is an audit table that keep tracks of all changes.column D acts as the timestamp for that record.
For my query, I am only interested in changes in column A,B and D. After the query I would like to get the result as below:
Column A B D
100 300 T1
100 100 T4
100 300 T5
101 11 T6

Answer 1

I think Analytics might do what you want :
select col1, col2, last(col1) over (order by col1, col2) LASTROWVALUE
from table1
this way, LASTROWVALUE will contain de value of col1 for the last row, which you can directly compare to the col1 of the current row.
Look this URL for more info : http://www.orafaq.com/node/55

Answer 2

SELECT ROW_NUMBER() OVER(ORDER BY <Some column name>) rn,
Column1, <Some column name>, CompareColumn,
LAG(CompareColumn) OVER(ORDER BY <Some column name>) PreviousValue,
LEAD(CompareColumn) OVER(ORDER BY <Some column name>) NextValue,
case
when CompareColumn != LEAD(CompareColumn) OVER(ORDER BY <Some column name>) then CompareColumn||'-->'||LEAD(CompareColumn) OVER(ORDER BY <Some column name>)
when CompareColumn = LAG(CompareColumn) OVER(ORDER BY <Some column name>) then 'NO CHANGE'
else 'false'
end
FROM <table name>
You can use this logic in a loop to change behaviour.

Answer 3

Hi It's not very clear what exactly yuo want to accomplish. But maybe you can fetch the results of the original query in a PLSQL collection and use that to do your comparison.

Answer 4

What exactly are you doing the row comparison for? Are you looking to eliminate duplicates, or are you transforming the data into another form and then returning that?
To eliminate duplicates, look to use GROUP BY or DISTINCT functionality in your SELECT.
If you are iterating over the initial data and transforming it in some way then it is hard to do it without using a temporary table - but what exactly is your problem with the temp table? If you are concerned about the performance of a cursor then maybe you could do one outer SELECT that compares the results of two inner SELECTs - but the trick is that the second SELECT is offset by one row, so you achieve the requirement of comparing row 1 against row2, etc.

Answer 5

I think you are complicating things with the temp table.
It can be made using a cursor and 2 temporary variables.
Here is the pseudo code:
declare
v_temp_a%xyz;
v_temp_b%xyz;
i number;
cursor my_cursor is select xyz from xyz;
begin
i := 1;
for my_row in my_cursor loop
if (i = 1)
v_temp_a := my_row;
else
v_temp_b := v_temp_a;
v_temp_a := my_row;
/* at this point v_temp_b has the previous row and v_temp_a has the currunt row
compare them and put whatever logic you want */
end if
i := i + 1;
end loop
end