Re: Lowest 2 items per

On 2012-06-01 5:44 PM, Relyea, Mike wrote:
>> -----Original Message-----
>> From: David Johnston [mailto:polobo(at)yahoo(dot)com]
>> Sent: Friday, June 01, 2012 11:13 AM
>> To: Relyea, Mike
>> Cc:<pgsql-sql(at)postgresql(dot)org>
>> Subject: Re: [SQL] Lowest 2 items per
>>
>>
>> I would recommend using the "RANK" window function with an appropriate
>> partition clause in a sub-query then in the outer query you simply
> WHERE
>> rank<= 2
>>
>> You will need to decide how to deal with ties.
>>
>> David J.
>
>
> David,
>
> I've never used window functions before and rank looks like it'd do the
> job quite nicely. Unfortunately I'm using 8.3 - which I should have
> mentioned in my original request but didn't. Window functions weren't
> introduced until 8.4 from what I can tell.
>
> Mike
>
Mike,

try following query it's a variation on a top N ( = 3) query
SELECT FRS.*
FROM (
SELECT PRN.make
,PRN.model
,CSM.color
,CSM.type
,cost/yield rank
FROM consumable CSM
,printers PRN
,printersandconsumable PCM
WHERE 1 = 1
AND PCM.printerid = PRN.printerid
AND PCM.consumableid = CSM.consumableid
group by PRN.make
,PRN.model
,CSM.color
,CSM.type
) FRS
WHERE 3 > (
SELECT COUNT(*)
FROM (
SELECT PRN.make
,PRN.model
,CSM.color
,CSM.type
,cost/yield rank
FROM consumable CSM
,printers PRN
,printersandconsumable PCM
WHERE 1 = 1
AND PCM.printerid = PRN.printerid
AND PCM.consumableid = CSM.consumableid
group by PRN.make
,PRN.model
,CSM.color
,CSM.type
) NXT
WHERE 1 = 1
AND NXT.make = FRS.make
AND NXT.model= FRS.model
AND NXT.color= FRS.color
AND NXT.type = FRS.type
AND NXT.cost <= FRS.cost
)