Re: Bucketing Row Data in columns

I would be suspicious of this sort of solution of turning rows into
columns by mean of a series of correlated sub-selects. Once the data
set gets large and the number of columns goes over 2 or 3 this will in
all likelihood not perform well.
I had the pleasure of re-writing a "report" which was based on count()
(similar to sum()) per user_id with the counts going into various
columns per user. 18000 users, a dozen columns from table of 2 million
rows, report took >1,000,000 seconds (yes almost 12 days) to complete.
Re-write runs in 5-10 minutes (now at 10M rows) by getting the counts as
rows (user, item, count) into a temp table and making the columns from
the temp table (pl/psql) Getting the counts takes half the time, making
the flattened report takes half the time.

Oliveiros Cristina wrote:
> Hello, Sandeep,
>
> I am not sure if this is what you want.
>
> I came up with this query
>
> SELECT *
> FROM (SELECT user_id,SUM(amount) as day1 FROM t1 WHERE
> create_timestamp = '2009-1-1' GROUP BY "user_id") a
> NATURAL FULL JOIN (SELECT user_id,SUM(amount) as day2 FROM t1 WHERE
> create_timestamp = '2009-1-2' GROUP BY "user_id") b
> NATURAL FULL JOIN (SELECT user_id,SUM(amount) as day3 FROM t1 WHERE
> create_timestamp = '2009-1-3' GROUP BY "user_id") c
>
> The solution is not totally correct because it returns NULL in the
> places you return 0.
> It seems the SUM() returns NULL when it gets an all NULL column...
> Is it problematic for your application ?
>
> Also, i 'm not sure if I fully understand your last sentence
> /lets assume the buckets are fixed i.e 3 only. but I wish to get them
> unlimited i.e day 1 to day 20./
>
> You say that the buckets are fixed at 3. So, you mean the table output
> will always have 4 columns? 3 days plus one for user_id ?
> If you want 20 buckets it must be a different query...
>
> Could you please clarify what you mean when you say that you want to
> get a bucket unlimited ?
>
> Best,
> Oliveiros
>
> ----- Original Message -----
>
> *From:* Sandeep <mailto:gibsosmat(at)gmail(dot)com>
> *To:* pgsql-sql(at)postgresql(dot)org <mailto:pgsql-sql(at)postgresql(dot)org>
> *Sent:* Wednesday, June 24, 2009 5:39 PM
> *Subject:* [SQL] Bucketing Row Data in columns
>
> Hi all,
> I need help on creating a sql, not a problem even if its pl/sql
>
> I have orders table schema is as follow
>
> orders(order_id,user_id, create_timestamp, amount)
>
> and I want to generate a report like
> for the past 3 days bucketing purchases i.e SUM(amount) every day
> in columns
> i.e result will be having these columns.
>
> (user_id, amount_day1, amount_day2, amount_day3)
>
> ex:
> am leaving order_id assume they are auto incrementing and unique,
> date format dd/mm/yyyy
> (user_id, create_timestamp, amount)
> (user1, 01/01/2009,100)
> (user1, 01/01/2009,100)
> (user2, 01/01/2009,100)
> (user2, 02/01/2009,100)
> (user2, 02/01/2009,100)
> (user1, 02/01/2009,100)
> (user2, 03/01/2009,100)
> (user2, 03/01/2009,100)
> (user3, 03/01/2009,100)
>
>
> result
>
> (user_id, amount_day1, amount_day2, amount_day3)
> (user1, 200, 200, 0)
> (user2, 100, 200, 200)
> (user3, 0, 0, 100)
>
>
> hope you guys got what I am trying to generate through sql.
>
> I could get this data in each row, but I want it in columns.
> Can anyone help me on this? lets assume the buckets are fixed i.e
> 3 only. but I wish to get them unlimited i.e day 1 to day 20.
>
> Regards
> Sandeep Bandela
>