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Finding NULL Values

You can use a WHERE clause to filter values by whether or not they're NULL.

IS NULL

SELECT name FROM users WHERE first_name IS NULL;

IS NOT NULL

SELECT name FROM users WHERE first_name IS NOT NULL;

Assignment

The way we store transactions at CashPal is interesting. We store a user_id field on the transactions table. That user is the "owner" of the transaction, and a user_id is never null.

Whenever the owner of the transaction receives money, the sender_id will not be null – it will be the user ID of the sender. The recipient_id will be null.

Whenever the owner of the transaction sends money, the recipient_id will not be null – it will be the user ID of the recipient. The sender_id will be null.

Select all the rows and their columns from the transactions table where the owner of the transactions is receiving money.