Please tell me why in this query displays 2500 and not 5000.

select sum (Price) from Products WHERE ID IN
(Select ID_Product From Order_Products WHERE ID_Order = 1)

Products Table
ID | Price
1 | 2500.

Order_Products Table
ID | ID_Order | ID_Product.
1 | 1 | 1
2 | 1 | 1

Answer 1

Because it is necessary to teach normal joyans. And subqueries are such joyans for the poor.

Here it turns out a request

select sum (Price) from Products Where ID in (1,1)

which is actually syntax sugar for request

select sum (Price) from Products Where id = 1 or id = 1

which returns 1 line

And you need a request that returns 2 lines. And it will make the usual simple joyne

select sum (Price) from Order_Products Op, Products P
Where p.ID = OP.ID_Product and id_order = 1