Question

I know just about the basic usage of COUNT(*) and I wonder if I can use it or some other function to get the following result.

I have a table with people and the products they have purchased (product_id_). I have second table which maps each product_code to a single product_category.

Using a simple SELECT I can combine both tables to get:

first last   product_code product_category
John  BGood  100          Food
John  BGood  29           Beverage
John  BGood  30           Beverage
Rita  Black  25           Fashion
Betty Rock   36           Electronics
Betty Rock   72           Food
Betty Rock   100          Food
Betty Rock   36           Electronics

But what I would like is to count for each person the number of products it purchased from each category. product_category is an enum with 5 possible values (the four above and Other). I would like to get a table like:

first last   product_category count
John  BGood  Food             1
John  BGood  Beverage         2
John  BGood  Fashion          0
John  BGood  Electronics      0
John  BGood  Other            0
Betty ...

Answer 1

SELECT first, last, product_category, COUNT(product_code)
FROM <table>
ORDER BY last, first
GROUP BY first, last, product_category