MySQL join table return only one match - mysql

Question

I'm struggling the the JOIN in a MySQL query. Somehow I can't find out why my result is not what I want.
I have two tables, a table orders and a table products. The table product holds the order.id of the order. So a order can have more than one products, so for example the table products holds two records for a order.
The result I need is all orders where a product holds a VAT of 21.
Table example.
orders
id | customer
---------------
1 | John Doe
2 | Hello World
order_products
id | order_id | product | vat
1 | 1 | Porsche 911 GT4 | 21
2 | 1 | Audi R8 LMS | 21
3 | 1 | Ferrari Enzo | 19
3 | 2 | Bugatti Veyron | 19
No I want all orders where the products have a VAT of 21. So I will do a LEFT JOIN on the table order_products:
SELECT orders.id, orders.customer, order_products.product FROM orders LEFT JOIN order_products ON orders.id = order_products.order_id WHERE order_products.vat = '21'
This returns the following:
1 John Doe Porsche
1 John Doe Audi R8 LMS
But I only need one result because the orders.id is important for me, not all products in the order. I only join on the order_products to get the orders with only VAT 21. At the moment I ran out of options on how to fix this. Even after reading several topics about joins on this site and other sites.

Answer 1

First, you aren't going to return any orders that don't have products, so there is no need for a left join...an inner join is fine.
If the orders_product is not important to you, you can use a subquery and not select any columns from the orders_product. With your current query, you're selecting a column though.
Something like...
SELECT id, customer
FROM orders
WHERE order_id IN (SELECT order_id FROM order_products
WHERE order_products.vat = '21');
If you prefer not to use a correlated subquery, you can use a group by or distinct
SELECT orders.id, orders.customer
FROM orders
INNER JOIN order_products ON orders.id = order_products.order_id
WHERE order_products.vat = '21'
GROUP BY orders.id, orders.customer;
or...
SELECT DISTINCT orders.id, orders.customer
FROM orders
INNER JOIN order_products ON orders.id = order_products.order_id
WHERE order_products.vat = '21';

Answer 2

If you only care about the orders then you can group by the order id:
SELECT orders.id, orders.customer, order_products.product
FROM orders
LEFT JOIN order_products ON orders.id = order_products.order_id
WHERE order_products.vat = '21'
GROUP BY orders.id;
However note that order_products.product will only be one of the products. If you wish to display all of the products but in the one column you can user GROUP_CONCAT:
SELECT orders.id, orders.customer, GROUP_CONCAT(order_products.product)
FROM orders
LEFT JOIN order_products ON orders.id = order_products.order_id
WHERE order_products.vat = '21'
GROUP BY orders.id;
This will return:
1 John Doe Porsche, Audi R8 LMS

Answer 3

SELECT DISTINCT o.id
, o.customer
FROM orders o
JOIN order_products op
ON op.order_id = o.id
WHERE op.vat = 21;