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  1. #1
    Join Date
    Sep 2015

    Unanswered: Excluding from results based on criteria - how to?

    I have an issue whereby I need to measure the number of people who had membership at any one time. So in the scenario, I need to know how many people have a full membership at a point in time (dotted line). In this instance, I want to ensure that Person B is only counted once instead of twice however the only way I can think of doing it is counting the number of start dates with no end date at a point in time. This however currently gives me a result of 3 instead of 2. How can I avoid Person B being counted?
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    Does this make sense? Whats the best way in Postgres to calculate this?

  2. #2
    Join Date
    Nov 2015
    If these people have distinct identities and each enrolment has an effective start and end date then you can use something like:

    select count(distinct id) from enrolments where now() between start_date and end_date;

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