Re: Query to get the min of the total

----- Original Message -----

From: Marta Pérez Romero

To: pgsql-novice@postgresql.org

Sent: Friday, May 04, 2012 10:43 AM

Subject: [NOVICE] Query to get the min of the total

Hi All,

I am trying to do something but cannot find the way.

Hopefully you have some suggestions :)

I have two tables, as follows:

pets: with these columns: petcode, petname, petprice, petfamily

sales: with these columns: salescode, petcode, quantity

The pets table contains all the pets in my pet shop, with the code of the pet, its name, its price and the family it belongs to.

So for example:

petcode | petname | petprice  | petfamily

------------------------------------------------------------

1  | canary | 5.00  | birds

2  | retriever  | 12.00  | dogs

3  | siamese  | 28.00  | cats

4  | sparrow  | 7.00  | birds

5  | poodle  | 16.00  | dogs

The sales table tracks all the sales in the shop, with the code of the sale, the code of the pet that was bought, and the quantity of this pet bought.

For example:

salescode  | petcode  | quantity

----------------------------------------------

1  | 1  | 2

2  | 4  | 5

3  | 5  | 1

4  | 2  | 3

5  | 5  | 8

6  | 1  | 4

Now, I need to build a query that returns the least sold pet, in quantity. It will include the pet name and the quantity sold.

So in the example above it will be:

petname  | quantity

retriever | 3

Now, the problem I have is that I can´t work with nested aggregations.

First I need to get the total quantity by petcode (which will be the sum of quantity). And then get the MIN of the SUM of quantity, which I don´t know how to do.

This is the query so far: 

SELECT 

  pets.petname,

  sum(sales.quantity)

  

FROM  sales INNER JOIN  pets ON  sales.petcode= pets.petcode

GROUP BY 

   pets.petname

  

HAVING SUM(sales.quantity)=(SELECT MIN(quantity) FROM sales)

ORDER BY  pets.petname;

But it does not return any result. How can I do it?

Thanks very much