Question

I have to find the difference in the value of a single column of table as current row value-previous row value for some ‘n’ number of rows in one column and also I don’t have ID to use as reference for increment

date: box_count : total_no_of_boxes_used

1/12/12 2   2
2/12/12 8   6
3/12/12 14  6

I have box_count column and I am trying to get total_no_of_boxes_used column.
Please help me.

Thanks in advance

Answer 1

Given your records are sequential by date…..

• SQLFIDDLE DEMO

Query:

select a.date, a.bc, case when (a.bc-b.bc) is null then a.bc else a.bc-b.bc end tot
from tt a
left join 
tt b
on a.date > b.date
group by b.date
;

Results:

DATE                            BC      TOT
December, 01 2012 00:00:00+0000     2   2
December, 02 2012 00:00:00+0000     8   6
December, 03 2012 00:00:00+0000     14  6
December, 04 2012 00:00:00+0000     23  9