270. NULL functions

The NULL value is not a number, string, date, timestamp, array or JSON object. It’s just NULL, this is why it has its own functions:

COALESCE(val1, val2, …)

The COALESCE() function accepts the arbitrary number of arguments and returns the first non-NULL one. It’s really handy for setting default values:

WITH reading_stats AS ( SELECT user_id, COUNT(*) books_count FROM books_users GROUP BY 1 ) SELECT u.id AS user_id, COALESCE(books_count, 0) AS books_count FROM users u LEFT JOIN reading_stats r ON u.id = r.user_id

NULLIF(val1, val2)

The NULLIF()...

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