Question

A store maintains data on customers, products and purchase records in three tables: CUSTOMER, PRODUCT, PURCHASE. The store manager wants to know which product is on its maximum discount for each category.Write a query to print the following fields for each category, ordered by productID ascending : category, product_id and discount for the product that has the max discount in category. In the case of multiple products having same max discount within a category, print the product with minimum product_id

CUSTOMER
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CUSTOMER_ID INT
CUSTOMER_NAME STRING
CITY STRING
STATE STRING

PRODUCT
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PRODUCT_ID INT
PRODUCT_NAME STRING
CATEGORY STRING
PRICE INT
DISCOUNT INT
AVAILABLE INT

PURCHASE
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ID INT
CUSTOMER_ID INT
PRODUCT_ID INT
PURCHASE_DATE DATE
  

The part I would need help with would be how to compare the max discounts and print the min product_id, if the max discount is equal for each category.

Answer 1

Query to print the following fields for each category, ordered by productID ascending : category, product_id and discount for the product that has the max discount in category. In the case of multiple products having same max discount within a category, print the product with minimum product_id

select Category, DISCOUNT , min(PRODUCT_ID) from
(select p.Category, p.DISCOUNT , PRODUCT_ID from Product p ,
(SELECT CATEGORY , max(DISCOUNT) DISCOUNT FROM Product group by Category) max_discount_cat where p.Category = max_discount_cat.Category and p.DISCOUNT = max_discount_cat.DISCOUNT) group by Category, DISCOUNT order by PRODUCT_ID;

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SELECT CATEGORY , max(DISCOUNT) DISCOUNT FROM Product group by Category returns the Category and maximum discount for that category

(select p.Category, p.DISCOUNT , PRODUCT_ID from Product p ,
(SELECT CATEGORY , max(DISCOUNT) DISCOUNT FROM Product group by Category) max_discount_cat where p.Category = max_discount_cat.Category and p.DISCOUNT = max_discount_cat.DISCOUNT) returns Category, discount and Product Id of all products in each category having the discount as the maximum discount

select Category, DISCOUNT , min(PRODUCT_ID) from
(select p.Category, p.DISCOUNT , PRODUCT_ID from Product p ,
(SELECT CATEGORY , max(DISCOUNT) DISCOUNT FROM Product group by Category) max_discount_cat where p.Category = max_discount_cat.Category and p.DISCOUNT = max_discount_cat.DISCOUNT) group by Category, DISCOUNT order by PRODUCT_ID; returns the Category, Discount and minimum product id from the result set we got in the previous step.