← SQL Analyst Starter
Lesson 4 of 4
Treat NULL explicitly
Distinguish missing values from zero and blank text.
Do the work
- NULL is an unknown value, not 0 or empty text.
- Use IS NULL rather than = NULL.
- Use COALESCE only when the output contract declares a default.
See the method
Riley has NULL email; Casey has an empty email.
Read every demonstration step
- Riley has NULL email; Casey has an empty email.
- IS NULL selects only Riley.
- COALESCE(region, 'Unknown') gives an explicit output label.
Practice independently
Exercise 1
Find genuinely missing emails
Open practice →Exercise 2Label an unknown order region
Open practice →Take it further
Write separate diagnostics for NULL email and empty email.