On 5/28/2013 11:04 AM, Torsten Grust wrote:
On 25 May 2013, at 9:19, Bill MacArthur wrote (with possible deletions):
[...]
select * from test;
id | rspid | nspid | cid | iac | newp | oldp | ppv | tppv
----+-------+-------+-----+-----+------+------+---------+---------
1 | 2 | 3 | 4 | t | | | |
1 | 2 | 3 | | | 100 | | |
1 | 2 | 3 | | | | 200 | |
1 | 2 | 3 | | | | | | 4100.00
1 | 2 | 3 | | | | | | 3100.00
1 | 2 | 3 | | | | | -100.00 |
1 | 2 | 3 | | | | | 250.00 |
2 | 7 | 8 | 4 | | | | |
(8 rows)
-- I want this result (where ppv and tppv are summed and the other distinct
values are boiled down into one row)
-- I want to avoid writing explicit UNIONs that will break if, say the "cid" was entered
as a discreet row from the row containing "iac"
-- in this example "rspid" and "nspid" are always the same for a given ID,
however they could possibly be absent for a given row as well
id | rspid | nspid | cid | iac | newp | oldp | ppv | tppv
----+-------+-------+-----+-----+------+------+---------+---------
1 | 2 | 3 | 4 | t | 100 | 200 | 150.00 | 7200.00
2 | 7 | 8 | 4 | | | | 0.00 | 0.00
One possible option could be
SELECT id,
(array_agg(rspid))[1] AS rspid, -- (1)
(array_agg(nspid))[1] AS nspid,
(array_agg(cid))[1] AS cid,
bool_or(iac) AS iac, -- (2)
max(newp) AS newp, -- (3)
min(oldp) AS oldp, -- (4)
coalesce(sum(ppv), 0) AS ppv,
coalesce(sum(tppv),0) AS tppv
FROM test
GROUP BY id;
This query computes the desired output for your example input.
There's a caveat here: your description of the problem has been
somewhat vague and it remains unclear how the query should
respond if the functional dependency id -> rspid
does not hold. In this case, the array_agg(rspid)[1] in the line
marked (1) will pick one among many different(!) rspid values.
I don't know your scenario well enough to judge whether this would be
an acceptable behavior. Other possible behaviors have been
implemented in the lines (2), (3), (4) where different aggregation
functions are used to reduce sets to a single value (e.g., pick the
largest/smallest of many values ...).
Cheers,
--Torsten
Slick! Interesting usage scenarios for those aggregate functions array_agg and
bool_or, one new to me and the other rarely used, and even for min and max
which I never thought of using in this sense.
I tried not be be overbearing with descriptive details hoping that somebody
would look at the simplistic case and offer what might be considered an obscure
way of implementing some of Postgres's handy features for an unusual problem.
With a little tweaking for the exact nature of the environment, I am good to go.
Thank you, Torsten!
Bill MacArthur
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