WHERE subscription_start < ‘2017-01-01’
(subscription_end IS NULL)
OR (subscription_end >= ‘2017-01-01’)
When calculating Churn on the second problem in the “Single Month I” section, I’m having trouble understanding why the
“OR (subscription_end >= '2017-01-01)”
is needed. If the denominator is looking for current accounts that haven’t cancelled in January, why is there a filter where the subscription HAS ended, instead of solely NULL?