Two left joins gives me untrue data(double data?) with MySQL

Question

This is my query:

SELECT `products`.*, SUM(orders.total_count) AS revenue,
    SUM(orders.quantity) AS qty, ROUND(AVG(product_reviews.stars)) as avg_stars 
FROM          


        

Answer 1

The problem is that the product_reviews and orders table can have more that one row per product id. One way you can fix this is to use a subquery:

SELECT `products`.*, 
  o.revenue,
  o.qty, 
  ROUND(avg_stars) as avg_stars 
FROM `products` 
LEFT JOIN
(
  select `product_id`, 
    sum(total_count) revenue,
    sum(quantity) qty
  from `orders`
  where `status` in ('delivered', 'new')
  group by `product_id`
) o
  ON `products`.`id` = o.`product_id`
LEFT JOIN
(
  select product_id, avg(stars) avg_stars
  from product_reviews
  group by product_id
) pr
    ON (products.id = pr.product_id)
ORDER BY products.ID DESC
LIMIT 10
OFFSET 0