如何使用来自两个不同表的列创建 SQL 对象？

Question

I have an 'Orders' table and a 'Records' table.

Orders table has the following columns:

order_id       
order_date        
seller        
order_price

Records table has the following columns:

order_id        
record_created_at         
record_log

The record_log shows whether the order was 'approved' or 'declined'.

I'm trying to create a new table with the last two columns showing 'order_approved_rate_sum', which is the rate of number of orders approved out of number of orders placed.

MY current query is:

SELECT seller
     , o.order_id
     , COUNT(DISTINCT o.order_id) AS approved
  FROM records r
     , orders o
 WHERE l.order_id IN (
SELECT order_id
    FROM records
    WHERE record_log = 'approved')
 GROUP 
    BY merchant_name
;

I'm trying to start by getting the total number of approved orders but this query fetches the wrong numbers.

What am I doing wrong?

Answer 1

try the below -

SELECT seller, COUNT(DISTINCT o.order_id) AS approved 
FROM records r inner join orders o 
on r.order_id=o.order_id
where record_log = 'approved'
GROUP BY seller

Answer 2

First, if you insist on doing the query this way instead of using INNER JOIN, you need to remember to include o.order_id=r.order_id in your WHERE clause. Otherwise, you should use the INNER JOIN syntax.

Second, your GROUP BY clause should include all fields from the SELECT clause that are not part of an aggregate. I am going to assume when you say merchant_name you meant seller. So in your query the GROUP BY should be GROUP BY seller,o.order_id

Third,having the order_id as both a field and an aggregate is going to give you the count of each order_id individually, which is most likely going to be 1 each time.

Something close to what you were doing that should work is the following:

SELECT o.seller AS merchant,
      COUNT(DISTINCT o.order_is) AS approved
FROM records r, orders o
WHERE r.order_id = o.order_id
AND
o.order_id IN (SELECT order_id FROM records WHERE record_log='approved')
GROUP BY o.seller

However, it would be better to do:

SELECT o.seller AS merchant,
       COUNT(DISTINCT o.order_id) AS approved
FROM records r INNER JOIN orders o
ON r.order_id=o.order_id
WHERE r.record_log = 'approved'
GROUP BY o.seller;

Answer 3

If you're trying to get the approval rate by seller, then your query could look like this...

    with cte1 as
    (select o.seller, count(distinct o.order_id) as approved_orders
    from orders o
    join records r
        on r.order_id = o.order_id
    where r.record_log = 'approved'
    group by o.seller
    ), 
    cte2 as
    (
    select o.seller, count(distinct o.order_id) as all_orders
    from orders o
    join records r
        on r.order_id = o.order_id
    group by o.seller
    )
    select cte2.seller, coalesce((cte1.approved_orders / cte2.all_orders),0) as approval_rate
    from cte2
    left join cte1
        on cte1.seller = cte2.seller