MediumSQL challenge #182JOIN

Find Orders Whose Payment Amount Differs from the Order Total

Return the orders whose recorded payment amount is not equal to the order total.

The challenge runs on the SQLabHub practice database (SQLite) and uses the orders and payments tables. You can solve it in the browser, with nothing to install.

Solve This SQL Challenge

The task

Find orders where payment amount differs from order total.

A correct answer returns 200 rows with 3 columns: id, total, amount.

Tables used in this challenge

`orders` 200 rows

id INTEGER (PK) · user_id INTEGER · total REAL · discount REAL · item_count INTEGER · status TEXT · order_date TEXT · shipped_date TEXT · shipping_city TEXT · shipping_country TEXT

First 3 rows of the orders table
id	user_id	total	discount	item_count	status	order_date	shipped_date	shipping_city	shipping_country
1	43	2638.11	0.25	3	cancelled	2024-04-24	NULL	Los Angeles	USA
2	8	2947	0.19	5	delivered	2024-03-15	2023-04-09	Chicago	USA
3	136	683.24	0.08	2	delivered	2023-02-15	2023-07-10	Los Angeles	USA

`payments` 200 rows

id INTEGER (PK) · order_id INTEGER · user_id INTEGER · amount REAL · method TEXT · status TEXT · paid_at TEXT · transaction_id TEXT

First 3 rows of the payments table
id	order_id	user_id	amount	method	status	paid_at	transaction_id
1	46	105	921.62	Gift Card	success	2022-05-18	TXNHTN4GIK5L
2	157	37	1723.82	Bank Transfer	success	2024-11-11	TXNKJPIXJOFP
3	45	36	978.76	Bank Transfer	refunded	2023-10-24	TXNU2RW4MK1R

The first rows of each table are shown. See how all the tables relate on the database schema page.

Expected output

Expected output of the challenge
id	total	amount
46	1914.56	921.62
157	4882	1723.82
45	4070.29	978.76
104	1700.63	1579.17
18	4259.07	538.06

First 5 of 200 rows. This is the output of the model solution on the practice database. The task does not fix a sort order, so your rows may come back in a different order.

What you practise

Choosing exactly which columns a query returns
Filtering rows with a WHERE condition
Combining rows from two tables on a matching key with an inner join

Hint and approach

Try the challenge first. Open these only when you need them.

Show the hint

JOIN payments

Show the step-by-step approach

How the model solution is built, in the order the database evaluates it:

Read from the orders table.
Join payments on orders.id = payments.order_id.
Filter in WHERE: keep the rows where orders.total is not equal to payments.amount.
Return only the columns orders.id, orders.total and payments.amount.

Model solution

Checking your session…

What to watch for

This is a reconciliation query: join on the key, then filter on the inequality. In this dataset totals and payment amounts are generated independently, so every joined row differs; on real data the result is the exception list.

INNER JOIN. An inner join drops rows that have no partner on the other side, and it repeats a row once for every match, which inflates SUM and COUNT.
WHERE. WHERE is evaluated before the SELECT list, so it cannot use a column alias defined there or the result of an aggregate.