Re: Lowest 2 items per - Mailing list pgsql-sql

A few of approaches to solve this problem:

http://sql-ex.com/help/select16.php

01.06.2012, 18:34, "Relyea, Mike" <Mike.Relyea@xerox.com>:
> I need a little help putting together a query.  I have the tables listed
> below and I need to return the lowest two consumables (ranked by cost
> divided by yield) per printer, per color of consumable, per type of
> consumable.
>
> CREATE TABLE printers
> (
>   printerid serial NOT NULL,
>   make text NOT NULL,
>   model text NOT NULL,
>   CONSTRAINT printers_pkey PRIMARY KEY (make , model ),
>   CONSTRAINT printers_printerid_key UNIQUE (printerid ),
> )
>
> CREATE TABLE consumables
> (
>   consumableid serial NOT NULL,
>   brand text NOT NULL,
>   partnumber text NOT NULL,
>   color text NOT NULL,
>   type text NOT NULL,
>   yield integer,
>   cost double precision,
>   CONSTRAINT consumables_pkey PRIMARY KEY (brand , partnumber ),
>   CONSTRAINT consumables_consumableid_key UNIQUE (consumableid )
> )
>
> CREATE TABLE printersandconsumables
> (
>   printerid integer NOT NULL,
>   consumableid integer NOT NULL,
>   CONSTRAINT printersandconsumables_pkey PRIMARY KEY (printerid ,
> consumableid ),
>   CONSTRAINT printersandconsumables_consumableid_fkey FOREIGN KEY
> (consumableid)
>       REFERENCES consumables (consumableid) MATCH SIMPLE
>       ON UPDATE CASCADE ON DELETE CASCADE,
>   CONSTRAINT printersandconsumables_printerid_fkey FOREIGN KEY
> (printerid)
>       REFERENCES printers (printerid) MATCH SIMPLE
>       ON UPDATE CASCADE ON DELETE CASCADE
> )
>
> I've pulled together this query which gives me the lowest consumable per
> printer per color per type, but I need the lowest two not just the first
> lowest.
>
> SELECT printers.make, printers.model, consumables.color,
> consumables.type, min(cost/yield) AS cpp
> FROM printers
> JOIN printersandconsumables ON printers.printerid =
> printersandconsumables.printerid
> JOIN consumables ON consumables.consumableid =
> printersandconsumables.consumableid
> WHERE consumables.cost Is Not Null
> AND consumables.yield Is Not Null
> GROUP BY printers.make, printers.model, consumables.color,
> consumables.type
> ORDER BY make, model;
>
> After doing a google search I didn't come up with anything that I was
> able to use so I'm asking you fine folks!
>
> Mike
>
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