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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About SQL Habit
Hi, it’s Anatoli, the author of SQL Habit. 
SQL Habit is a course (or, as some of the students say, “business simulator”). It’s based on a story of a fictional startup called Bindle. You’ll play a role of their Data Analyst
and solve real-life challenges from Business, Marketing, and Product Management.
SQL Habit course is made of bite-sized lessons (you’re looking at one atm) and exercises. They always have a real-life setting and detailed explanations. You can immediately apply everything you’ve learned at work. 