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Correlated subquery mysql
Product ID | Product Name
===========+===============
1          | Tissues
2          | Glass

Sale ID    | Product ID | Quantity | Price
===========+============+==========+=============
1          | 1          | 1        | 55
2          | 2          | 1        | 60

Batch ID | Total Value | Quantity | Product ID
=========+=============+==========+==================
1        | 100         | 100      | 1
2        | 10          | 50       | 2
3        | 1           | 1        | 2

SELECT tblsale.product_id,
       tblproduct.product_name,
       SUM(tblsale.`quantity`) qty,
       SUM(tblsale.`Price`*tblsale.`quantity`) sales,
       (SELECT sum(total_value) / sum(quantity) VWAP
        FROM tblpurchases
        WHERE product_id = tblsale.product_id) average_price,
       (average_price * qty) cost,
       (sales-cost) profit
FROM   tblsale, tblproduct
WHERE tblproduct.product_id = tblsale.`product_id`
GROUP by tblsale.`product_id`

SELECT prod.product_id,
          prod.product_name,
          SUM(s.quantity) qty,
          SUM(s.Price * s.quantity) sales,
          SUM(pur.total_value) / SUM(pur.quantity) average_price,
          SUM(pur.total_value) / SUM(pur.quantity) * SUM(s.quantity) cost,
          SUM(s.Price * s.quantity) - (SUM(pur.total_value) / SUM(pur.quantity) * SUM(s.quantity)) profit
     FROM tblproduct prod
LEFT JOIN tblsale s ON prod.product_id = s.product_id
LEFT JOIN tblpurchases pur ON pur.product_id = prod.product_id
 GROUP BY s.product_id

SELECT p.product_id, p.product_name
         , SUM(s.quantity) number_of_sales
         , SUM(s.price) total_profit
         , SUM(pu.quantity) purchase_quantity
         , SUM(pu.value) purchase_value
         , (SUM(pu.quantity) - SUM(s.quantity)) number_in_stock
         , (SUM(s.price) - SUM(pu.value)) profit
         , (SUM(pu.value) / SUM(pu.quantity)) avarage_purchase_price
      FROM product p
 LEFT JOIN sales s ON s.product_id = p.product_id
 LEFT JOIN purchase pu ON pu.product_id = p.product_id
  GROUP BY s.product_id, pu.product_id