Buy
has a foreign key product_id
.
So in addition to SELECT * FROM products;
we are interested in getting the number of buys each product has.
Something along the lines of:
SELECT p.*, COUNT(buy.product_id) FROM product p INNER JOIN buy ON buy.product_id = p.id GROUP BY buy.product_id
should do the trick.
SELECT p.*,COUNT(b.product_id) FROM products p
INNER JOIN buy b ON p.id=b.product_id
GROUP BY b.product_id
Thats about all I can offer with the info you've posted. Table structure of both would help a ton if the above doesn't work.
Join
SELECT Products.*, COUNT(Buy.ID) AS Bought
FROM products
LEFT OUTER JOIN Buy ON products.ID = Buy.product_id
GROUP BY Buy.product_id
Subquery
SELECT
Products.*,
(SELECT COUNT(ID) FROM Buy WHERE product_id = Products.ID) AS Bought
FROM products
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