countIf
Description
The If combinator can be applied to the count
function to count the number of rows where the condition is true,
using the countIf aggregate combinator function.
Example Usage
In this example, we'll create a table that stores user login attempts,
and we'll use countIf to count the number of successful logins.
The countIf function will count only the rows where is_successful = 1 for each user.