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

> -----Original Message-----
> From: Oliveiros d'Azevedo Cristina
[mailto:oliveiros.cristina@marktest.pt]
> Sent: Friday, June 01, 2012 11:21 AM
> To: Oliveiros d'Azevedo Cristina; Relyea, Mike;
pgsql-sql@postgresql.org
> Subject: Re: [SQL] Lowest 2 items per
>
> Sorry, Mike, previous query was flawed.
>
> This is (hopefully) the correct version
>
> Best,
> Oliver
>
>  SELECT make, model, color,type, subquery1.cpp, min(cost/yield) as
cpp2  (
> 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
>  ) subquery1
>  JOIN
>  (
>  SELECT printers.make, printers.model, consumables.color,
> consumables.type,cost,yield  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
>  ) subquery2
> ON (subquery1.make = subquery2.make
> AND subquery1.model = subquery2.model
> AND subquery1.color = subquery2.color
> AND subquery1.type = subquery2.type)
>  WHERE subquery2.cost / subquery2.yield <> subquery1.cpp  GROUP BY
> subquery2.make,subquery2. model,
> subquery2.color,subquery2.type,subquery1.cpp
>  ORDER BY make, model;
>

Oliver,

I had to make a few grammatical corrections on your query to get it to
run, but once I did it gave me almost correct results.  It leaves out
all of the printer models that only have one consumable with a cost.
Some printers might have more than two black inks and some might have
only one.  Your query only returns those printers that have two or more.

Here's your query with the corrections I had to make
SELECT subquery2.Make, subquery2.Model, subquery2.Color,subquery2.Type,
subquery1.cpp, min(Cost/Yield) as cpp2
FROM(  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.ConsumableIDWHERE Consumables.Cost Is Not NullAND Consumables.Yield
IsNot NullGROUP BY Printers.Make, Printers.Model, Consumables.Color, 
Consumables.Type) subquery1JOIN(SELECT Printers.Make, Printers.Model, Consumables.Color,
Consumables.Type,Cost,Yield  FROM Printers  JOIN PrintersAndConsumables
ON Printers.PrinterID =  PrintersAndConsumables.PrinterID  JOIN
Consumables ON Consumables.ConsumableID =
PrintersAndConsumables.ConsumableIDWHERE Consumables.Cost Is Not NullAND Consumables.Yield Is Not Null) subquery2
ON (subquery1.Make = subquery2.Make
AND subquery1.Model = subquery2.Model
AND subquery1.Color = subquery2.Color
AND subquery1.Type = subquery2.Type)WHERE subquery2.Cost / subquery2.Yield <> subquery1.cpp  GROUP BY
subquery2.Make,subquery2.Model,
subquery2.Color,subquery2.Type,subquery1.cppORDER BY Make, Model;

Mike