HardSQL challenge #233JOINANTI JOINFILTER

Products With Zero Sales

Find products that never sold.

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

Solve This SQL Challenge

The task

Find products that never sold.

A correct answer returns 1 row with 10 columns: id, name, category, price, cost, stock, sku, status, rating, review_count.

Tables used in this challenge

`products` 120 rows

id INTEGER (PK) · name TEXT · category TEXT · price REAL · cost REAL · stock INTEGER · sku TEXT · status TEXT · rating REAL · review_count INTEGER

First 3 rows of the products table
id	name	category	price	cost	stock	sku	status	rating	review_count
1	Play Kitchen Deluxe	Toys	1786.38	589.51	257	SKU-000001	active	4	57
2	Micro-Cut Paper Shredder 8-Sheet	Office Supplies	907.93	281.46	131	SKU-000002	active	2.5	447
3	4K Dual Dash Camera	Automotive	568.89	204.8	176	SKU-000003	active	4.1	29

`order_items` 496 rows

id INTEGER (PK) · order_id INTEGER · product_id INTEGER · quantity INTEGER · unit_price REAL · subtotal REAL

First 3 rows of the order_items table
id	order_id	product_id	quantity	unit_price	subtotal
1	1	76	5	192.21	961.05
2	1	82	3	107.1	321.3
3	1	65	1	5.39	5.39

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	name	category	price	cost	stock	sku	status	rating	review_count
110	The Manager's Path	Books	1979.28	989.64	48	SKU-000110	active	4.9	381

The complete result: 1 row. This is the output of the model solution on the practice database.

What you practise

Filtering rows with a WHERE condition
Testing for missing values with IS NULL and IS NOT NULL
Keeping every row of the left table with LEFT JOIN, matched or not
Finding rows with no match using LEFT JOIN … IS NULL

Hint and approach

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

Show the hint

LEFT JOIN

Show the step-by-step approach

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

Read from the products table.
LEFT JOIN order_items on products.id = order_items.product_id. Rows from the left side that have no match are kept, with NULL in the joined columns.
Keep only the rows where the joined order_items columns are NULL. Those are the rows that found no match in the join.
Return every column of products.

Model solution

Checking your session…

What to watch for

Anti join. Test a column of the joined table that can never be NULL in a real row, normally its primary key. Testing a nullable column also returns matched rows where that column happens to be empty.
LEFT JOIN. A WHERE condition on the right-hand table removes the unmatched rows and turns the LEFT JOIN back into an inner join. Conditions on that table go in the ON clause.
IS NULL. Comparing with = NULL or <> NULL never matches any row. NULL has to be tested with IS NULL or IS NOT NULL.