3个表的SQL求和

Question

I have 4 tables that carry the following schema:

• Product (maker, model, type)
• PC (model, speed, ram, hd, price)
• Laptop (model, speed, ram, hd, screen, price)
• Printer (model, color,type, price)

Say I need to buy a PC, a Laptop, and a Printer all within a budget of $2K. What query should I use to find all of the available options that are underneath this budget?

Obviously for this problem I would need to look at all of the model #'s of PCs, Laptops, and Printers, and filter out the respective prices for each of those products.

But I'm not quite too sure what would be needed in my where clause to do this correctly.

select Product.model
from Product, PC, Laptop, Printer
where ... ???

Answer 1

I would guess you coud to something along these lines to start

Select * 
From PC, Laptop, Printer
Where (PC.price + Laptop.price + Printer.price) <= 2000

The implied join "From PC, Laptop, Printer" would make all the combinations since there not "joining Where", and then you just select the combinations that match you pricing criteria.

Answer 2

try

select Product.model
  from Product a, PC b, Laptop c, Printer d
 where a.model = b.model
   and a.model = c.model
   and a.model = d.model
   and b.model = c.model
   and b.model = d.model
   and c.model = d.model

This is a bad query, it is best to separate the query will get better performance

Answer 3

select PC.Model, PC.Price, Laptop.Model, Laptop.Price, Printer.Model, Printer.Price
from PC, Laptop, Printer
where (PC.price + Laptop.Price + Printer.Price) <= 2000

Does this work for you?

Answer 4

You can try CROSS JOIN or CROSS APPLY to get all the possible combinations and then filter out all that have price sum less than 2K$

Something like

SELECT
*
FROM PC
CROSS APPLY Laptop
CROSS APPLY Printer
WHERE
PC.price + Laptop.price + Printer.price < 2000