SQL查询汇总

Question

I have two tables

Unit

Unit_id
Unit_name
Unit_cost

Components

Component_id
Component_name
Unit_id

They are linked together by Unit_id .

Unit_id = 1 with name Unit 1 Name with a cost of 100 has a number of records in Component .

Unit_id = 2 with name Unit 2 Name and a cost of 200 also has a number of records in Component .

So the total cost depends on the number of records in the Component table matched with the unit_id in the Unit , coupled with the unit_price in the Unit table.

I need the single Unit_name of the one unit in the Unit table that has the highest total cost ( Unit.Unit_cost ). Note I just need the Unit_Name only, not total cost.

Would it be best to use a Top(1) in the query? How would the query look?

Answer 1

I think you want something like this:

select top (1) u.unit_name
from unit u join
     component c
     on c.unit_id = u.unit_id
group by u.unit_id, u.unit_name
order by sum(c.cost) desc;

Answer 2

assuming that unit cost should be multiplied by number of related components:

select top 1 name from(
select u.unit_name AS name, count(c.component_id) * u.unit_cost AS cost
from unit u join components c on u.unit_id = c.unit_id)
order by cost desc

In the inner query name and unit cost is calculated, at the outer query mname for unit that have max cost is selected. If cost should be calculated in some other way just change count(c.component_id) * u.unit_cost formula in the query