Question

In this sample database there are two tables, products and prices.
The goal is to find the highest and the lowest price for each product.

The price table can have either zero, one or two rows per product.

create table products(
    id int,
    name nvarchar(50)
)

create table prices(
    productId int,
    price int
)

insert into products (id, name) values (33,'bike')
insert into products (id, name) values (44,'car')
insert into products (id, name) values (55,'bus')

insert into prices (productId, price) values (33, 10)
insert into prices (productId, price) values (33, 40)
insert into prices (productId, price) values (44, 300)

The sql query should result in this:

productId  highPrice  lowPrice
33         40         10
44         300        NULL
55         NULL       NULL

Answer 1

This gives you the table that you’re looking for (I notice that the other answers don’t), in SQL Server 2005

select P.ID as ProductID, 
nullif(sum(case when idx=1 then price else 0 end), 0) as highPrice,
nullif(sum(case when idx=2 then price else 0 end), 0) as lowPrice  from
(
    select productid, price, row_number() over(partition by productID order by price desc) as idx from prices
) T
right join products P on T.productID = P.ID
group by P.ID