SQL practice: NULL: The Empty Box
Chapter 7 · 8 questions · included in full access
Question 1 · easy
Solve it in your browserFind all customers whose signup_date is filled in.
Question 2 · easy
Solve it in your browserFind all customers whose signup_date is empty.
Question 3 · medium
Solve it in your browserShow every employee's name and manager_id, displaying 'Top Boss' where there's no manager.
Question 4 · medium
Solve it in your browserWhich products have no thickness_mm? Why would that be, rather than being a mistake?
Question 5 · medium
Solve it in your browserShow each customer's name and signup date, with empty dates shown as 'Not recorded'.
Question 6 · medium
Solve it in your browserExplain in one sentence why WHERE thickness_mm <> 4.0 does not return the accessories.
Question 7 · hard
Solve it in your browserCount the customers two ways — COUNT(*) and COUNT(signup_date). Explain the difference in the numbers.
Question 8 · hard
Solve it in your browserThis query is trying to find customers with no signup date, but it returns nothing. Fix it.
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