Learn
While working with databases, it’s common to have empty or unknown “cells” in data tables. For example, in our first flights
table, we keep track of when flights arrive in a column called arr_time
:
In this table, the third flight was canceled and therefore did not have an arrive time. We’ll leave this cell empty, which is denoted as NULL
.
What do we do when we need to test whether a value is or is not null? We use the special keywords IS NULL
or IS NOT NULL
in the WHERE
clause (= NULL
does not work).
Instructions
1.
Count the number of rows from the flights
table, where arr_time
is not null and the destination is ATL
.
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