Counting number of records after applying Cartesian JOIN

[Admin]

Here is the problem:

All of the questions in this quiz pull from the open source Chinook Database. Please refer to the ER Diagram below and familiarize yourself with the table and column names to write accurate queries and get the appropriate answers.

How many records are created when you apply a Cartesian join to the invoice and invoice items table?

Here is my tentative solution:

SELECT *
FROM invoices
JOIN invoice_items
ON invoices.invoiceid = invoice_items.invoiceid

 

The solution that I am getting of 2240 records incorrect (Output limit exceeded, 25 of 2240 total rows shown).

Seeking help where I am going wrong.

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Reply

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Cartesian join == CROSS JOIN

https://www.sqlitetutorial.net/sqlite-cross-join/

The question is perhaps what happens when you apply a Cartesian JOIN to the two tables (no filtering with a WHERE clause). Your original query filters the results, so you’re not getting a proper count of rows.

Combine CROSS JOIN with COUNT.

SELECT COUNT(*)
FROM invoices
CROSS JOIN invoice_items

In SQLite JOIN without an ON clause is effectively the same as a CROSS JOIN.

[Author]

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