Sql query to get data diffrence of total in 2 tables

问题

I have two tables:

1. booking - records the order detail

   id | booking_amount
   -------------------
   1  |            150
   2  |            500
   3  |            400
   

2. payment - records the payment for order

   id | booking_id | amount
   ------------------------
   1  |          1 |    100
   2  |          1 |     50
   2  |          2 |    100
   

I want to find all bookings where the payments are not complete. With the above data, we expect the answer to be 2,3, because the sum of payments for booking_id=1 matches the corresponding booking_amount in the booking_table.

回答1:

To answer your question, you have 2 things you need to think about :

1. you want the total amount in your table payment by every booking row

2. you want to join your booking_amount table with payment.

---

Part 1 is quite simple:

SELECT sum(amount) as TotalP, booking_id FROM payment GROUP BY booking_id

Just a basic query with a simple aggregate function...

---

For part 2, we want to join booking_amount and payment; the basic JOIN would be:

SELECT * FROM booking b 
LEFT JOIN payment p ON b.id = p.booking_id

We do a LEFT JOIN because we may have some booking who are not in the payment table. For those bookings, you will get NULL value. We will use a COALESCE to replace the NULL values by 0.

---

The final query is this:

SELECT b.id, COALESCE(TotalP, 0),  b.booking_amount
FROM
 booking b
LEFT JOIN
 (SELECT sum(amount) as TotalP, booking_id FROM payment GROUP BY booking_id) as T
ON  b.id = T.booking_id
WHERE COALESCE(TotalP, 0) < b.booking_amount

回答2:

You need to use a outer join to combine your two tables and look for your conditions. Also, you will need to use SUM(..) function to get the sum of the amount for each id in the payment table.

Please try this:

select b.id from booking b 
left outer join -- cant be inner join because we lose id:3 in that case.
(
  select booking_id, SUM(amount) as Total 
  from payment group by booking_id
) p on b.id = p.booking_id
where b.booking_amount > Coalesce(Total,0) --Coalesce is required for such values coming NULL, like id:3, they will be assigned as 0.

来源：https://stackoverflow.com/questions/36452733/sql-query-to-get-data-diffrence-of-total-in-2-tables