SQL：在具有多个group by语句的两列上进行计算

Question

I have a table which has the following columns:

• user_id - includes duplicates

• product_id - includes duplicates

• purchases - number of purchases of given product_id

My table looks somewhat like this:

   user_id  date  product_id  purchases
0        1     1           1          4
1        1     2           1          0
2        1     3           2          0
3        1     4           2          0
4        2     1           1          1
5        2     2           1          0
6        2     3           1          1
7        3     1           2          0
8        3     2           3          0
9        4     1           5          1

My goal is to calculate the following metric:

% of products that were purchased at least once, grouped by user

For example: user 1 had 2 products, one of them got purchased at least once, the other one did not get purchased at all. So the metric would be the number of products that got purchased at least once / number of all products per user: 1/2 * 100 = 50%

I have little SQL experience so I do not have any legitimate code that could be corrected.

My desired output would be like this:

   user_id  total_products  products_with_purchases  metric
0        1               2                        1     50%
1        2               1                        1    100%
2        3               2                        0      0%
3        4               1                        1    100%

I would appreciate seeing a good practice solution to this problem. Many thanks!

Answer 1

select
    user_id,
    count(distinct product_id) as total_products,
    count(distinct case when purchases > 0 then product_id end) as products_with_purchases,
    100.00 * count(distinct case when purchases > 0 then product_id end)
        / count(distinct product_id) as metric
from T as t
group by user_id

https://rextester.com/EDSY39439

Answer 2

You can do this all in one query but this is the type of situation where it is easier to understand with sub-queries -- sql optimizer should make it fast.

select 
  user_id, 
  total_products,
  products_with_purchase,
  (products_with_purchase / total_products) * 100 as metric
from (
  select  -- group by user to get totals
    user_id, 
    count(product_id) as total_products,
    sum(case when purchases > 0 then 1 else 0 end) as products_with_purchase
  from ( -- group by user and product and get purchase items
    SELECT user_id, product_id, sum(purchases) as purchases
    FROM table
    GROUP BY user_id, product_id
  ) X
  group by user_id
) X2

Answer 3

I Am Mohit Sahni you can solve the above problem with the below SQL Code:

select 
user_id,
count(distinct product_id) as total_products,
sum(case when purchases = 0 then 0 else 1 end) as products_with_purchases,
((sum(case when purchases = 0 then 0 else 1 end))/count(distinct product_id))*100 as metric
from 
table
group by 
user_id