calculate rate of attribute by id sql - sql

Question

First, this is my table schema:
order_id, product_id, add_to_cart_order, reordered
My problem is calculate the rate of reordered by product. So we can see "add_to_cart_order" is useless, I don't know for "order_id". "reordered" can be have '1' and '0' value.
For the moment, I can have the count of "reordored" by product_id with
SELECT
product_id,
COUNT(reordered)
FROM
train
WHERE
reordered = '1'
GROUP BY
product_id;
and the count of occurrence of a product with
SELECT
product_id, COUNT(*)
FROM
train
GROUP BY
product_id;
I tried
SELECT
t1.product_id,
COUNT(t1.product_id) / (SELECT COUNT(reordered)
FROM train t2
WHERE t2.reordered = '1'
AND t1.product_id = t2.product_id
GROUP BY product_id)
FROM
train t1
GROUP BY
t1.product_id;
But it takes too much time (I don't know if it's the right request because I don't have results yet)

Answer 1

Is this what you are looking for?
SELECT Product_id, SUM(CASE WHEN reordered=1 THEN 1 ELSE 0 END ) /
COUNT(*) AS ReorderedRate
FROM
train
GROUP BY Product_id

Answer 2

Try this elegant
SELECT t1.product_id, SUM(CASE WHEN reordered = 1 THEN 1 ELSE 0 END) / COUNT(t1.product_id)
FROM train t1
GROUP BY t1.product_id;

Answer 3

I think the simplest method is to use AVG():
SELECT product_id,
AVG(CASE WHEN reordered = '1' THEN 1.0 ELSE 0 END)
FROM train
GROUP BY product_id;
If reordered is really a number that only takes on the values 0 and 1, then you can further simplify this to either:
SELECT product_id, AVG(reordered)
FROM train
GROUP BY product_id;
or:
SELECT product_id, AVG(reordered * 1.0)
FROM train
GROUP BY product_id;
The second is needed in databases where the average of an integer is returned as an integer.

Answer 4

this will compute for each product_id :
the number of lines in train cnt_prod
the number of lines in train cnt_prod_reorder that was reordered
SELECT t1.product_id, COUNT(t1.product_id) as cnt_prd,
COUNT(case when t.1.reordered='1' then 1 else NULL end ) as cnt_prd_reord
from train t1 group by t1.product_id;
So after you can do :
select st.product_id , st.cnt_prd , st.cnt_prd / st.cnt_prd_reord
from (
SELECT t1.product_id, COUNT(t1.product_id) as cnt_prd,
COUNT(case when t.1.reordered='1' then 1 else NULL end ) as cnt_prd_reord
from train t1 group by t1.product_id
) as st ;