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I tried to calculate difference between rows in a field using a query:
Illustrations: input:year,month,fixes output:increase year | month | fixes | increase ------+-------+----------+----------- 2006 | 04 | 1 | 0 2006 | 05 | 4 | 3 2006 | 06 | 3 | -1
Increase column as output by difference between adjacent rows in fixes.
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Method 1 : Using diff() method diff() method in base R is used to find the difference among all the pairs of consecutive rows in the R dataframe. It returns a vector with the length equivalent to the length of the input column – 1.
In the blue text, you can see the calculation of the SQL delta between two rows. To calculate a difference, you need a pair of records; those two records are “the current record” and “the previous year's record”. You obtain this record using the LAG() window function.
Discussion: To calculate the difference between the timestamps in PostgreSQL, simply subtract the start timestamp from the end timestamp. Here, it would be arrival - departure . The difference will be of the type interval , which means you'll see it in days, hours, minutes, and seconds.
col = tbl1. col); If you don't know which table has surplus rows or both have, you can either repeat the above query after switching table names, or: SELECT * FROM tbl1 FULL OUTER JOIN tbl2 USING (col) WHERE tbl2 col IS NULL OR tbl1.
This is what window functions are for:
select year, month, fixes, fixes - lag(fixes) over (order by year, month) as increase, from the_table; For more details please see the manual:
http://www.postgresql.org/docs/current/static/tutorial-window.html
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