Selection of two tables in sql

i post this question because i really can’t find a solution, i spent a day searching how to do this but i can’t make it work. that’s also because i’m new to sql and i need some help.

Situation :I have a database with 3 tables : Orders, Producs, Buys. In my C#/.NET application i need to display all products from one order, first here is the tables structure.

TABLE orders
    int id
    int Totalprice

Table products
    int id
    string name

Table buys
    int id
    int price
    int quantity
    int orderId
    int productId

Also, a buy can have many products and have 1 order, and an order can have many buys.

What i’m doing in my application :

In my C#/.NET application, this is what i do :

SELECT * FROM buys WHERE orderid=listview.selecteditem.orderid;

i store this results in a list and after this:

foreach(item in buys)//buys is the list stored from the previous query
        SELECT * FROM products WHERE productid = item.productId;

NOTE :this is only a pseudo code, because i didn’t start coding yet.

The problem :this code is working for me, but it’s a bit slow and need to perform two queries to get the expected result. i need a way to do this in one sql query. Thanks in advance

You may want to use


FROM buys b
JOIN orders o
ON = b.orderId
JOIN products p
ON = o.productId

Note also that is good practice to specify the fields instead of using *

As Michael suggested, you may want also to look at indexes
for better query performance.

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