SQL query to get Net Salse by every month

Question

I'm looking for a query to get monthly net sales I tried this far but I couldn't get what I want. this is my Order Table

+----------+-----------+--------+------------+---------------+-------------+-----------+---------+---------+
| orderID  | custID    | userID | orderDate  | paymentMethod | grossAmount | netAmount | cash    | balance |
+----------+-----------+--------+------------+---------------+-------------+-----------+---------+---------+
| INV-0001 | CUST-0001 | U-001  | 2020-05-01 | Cash Pay      |      525.00 |    525.00 |  550.00 |   25.00 |
| INV-0002 | CUST-0001 | U-001  | 2020-05-01 | Cash Pay      |      240.00 |    240.00 |  250.00 |   10.00 |
| INV-0003 | CUST-0001 | U-001  | 2020-05-01 | Cash Pay      |      220.00 |    220.00 |  250.00 |   30.00 |
| INV-0004 | CUST-0001 | U-001  | 2020-04-30 | Cash Pay      |      895.00 |    895.00 | 1000.00 |  105.00 |
| INV-0005 | CUST-0001 | U-001  | 2020-04-30 | Cash Pay      |      300.00 |    300.00 |  500.00 |  200.00 |
| INV-0006 | CUST-0001 | U-001  | 2020-04-30 | Cash Pay      |      230.00 |    230.00 |  250.00 |   20.00 |
+----------+-----------+--------+------------+---------------+-------------+-----------+---------+---------+

This is my CustomerReturn Table

+-------+----------+------------+--------+------------+-----------+-----------+-------------+
| retID | orderID  | itemCode   | userID | retDate    | returnQty | unitPrice | totalAmount |
+-------+----------+------------+--------+------------+-----------+-----------+-------------+
|     1 | INV-0001 | 1800232050 | U-001  | 2020-05-01 |      1.00 |    100.00 |      100.00 |
|     2 | INV-0002 | 1909873674 | U-001  | 2020-05-01 |      2.00 |     55.00 |      110.00 |
|     3 | INV-0004 | 1800232050 | U-001  | 2020-04-30 |      1.00 |    100.00 |      100.00 |
+-------+----------+------------+--------+------------+-----------+-----------+-------------+

the formula is (total of the monthly bill( Order .netAmount) - a total of monthly return ( CustomerReturn .totalAmount))

in need to get net sales every year of every month.

select orderDate,sum(netAmount)-sum(totalAmount) from `Order` o,CustomerReturn r where o.orderID=r.orderID GROUP BY orderDate;

when I run this query it shows me this

+------------+---------------------------------+
| orderDate  | sum(netAmount)-sum(totalAmount) |
+------------+---------------------------------+
| 2020-04-30 |                          795.00 |
| 2020-05-01 |                          555.00 |
+------------+---------------------------------+

but it should be Like this

+------------+---------------------------------+
| orderDate  | sum(netAmount)-sum(totalAmount) |
+------------+---------------------------------+
| 2020-04-30 |                         1425.00 |
| 2020-05-01 |                          775.00 |
+------------+---------------------------------+

please help me. Thank you.!

Answer 1

Your query is good, it is fetching all records when there is a match on OrderId in the table CustomerReturn and doing the sums as you requested, however there are no returns for the order INV-0003 , so this condition o.orderID=r.orderID is not valid when it comes to that record and it is ignoring that data. Doing a left join will fix the issue.

select 
    o.orderDate, 
    sum(o.netAmount)-sum(case when cr.totalAmount is null then 0 else cr.totalAmount end)
from 
    Orders o 
left join 
    CustomerReturn cr
on 
    o.orderID = cr.orderID
group by 
    o.orderDate

A left join will cause cr.totalAmount to have null values in case there is no match for o.orderID=r.orderID then we use this part; case when cr.totalAmount is null then 0 else cr.totalAmount end to fix that null issue.

Answer 2

Because you are joining on dates that is why you are not getting correct answer, as order date and return date can have different month. Better if you extract the month and then do sum as shown in below query, and here is the demo .

select
    o.mm as month,
    sum(total_net_amount - total_amount) as total
from
(
  select
    month(orderDate) as mm,
    sum(netAmount) as total_net_amount
  from Orders
  group by
      month(orderDate)
) o
join
(
  select
    month(retDate) as mm,
    sum(totalAmount) as total_amount
  from CustomerReturn
  group by
      month(retDate)
) cr
on o.mm = cr.mm
group by
    o.mm

Output:

*--------------*
|month | total |
*--------------*
| 5    |  775  |
| 4    |  1325 |
*--------------*

Answer 3

Learn to use proper, explicit, standard , readable JOIN syntax. As pointed out in another answer, you want a LEFT JOIN . That said, the simpler way to write the logic is:

select o.orderDate, 
       sum(o.netAmount)- coalesce(sum(cr.totalAmount, 0)) as net_amount
from Orders o left join 
     CustomerReturn cr
     on o.orderID = cr.orderID
group by o.orderDate;