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POSQL schema design question around relating 2 different types of ID's to one piece of information
 

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  1. POSQL schema design question around relating 2 different types of ID's to one piece of information
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    <p>I'm working on redesigning some parts of our schema, and I'm running into a problem where I just don't know a good clean way of doing something. I have an event table such as:</p> <pre><code>Events -------- event_id </code></pre> <p>for each event, there could be n groups or users associated with it. So there's a table relating Events to Users to reflect that one to many relationship such as:</p> <pre><code>EventUsers ---------- event_id user_id </code></pre> <p>The problem is that we also have a concept of groups. We want to potentially tie n groups to an event in addition to users. So, that user_id column isn't sufficient, because we need to store potentially either a user_id or a group_id.</p> <p>I've thought of a variety of ways to handle this, but they all seem like a big hack. For example, I could make that a participant_id and put in a participant_type column such as:</p> <pre><code>EventUsers ---------- event_id participant_id participant_type </code></pre> <p>and if I wanted to get the events that user_id 10 was a part of, it could be something like:</p> <pre><code>select event_id from EventUsers where participant_id = 10 and participant_type = 1 </code></pre> <p>(assuming that somewhere participant_type 1 was defined to be a User). But I don't like that from a philosophical point of view because when I look at the data, I don't know what the number in participant_id means unless I also look at the value in particpant_type.</p> <p>I could also change EventUsers to be something like:</p> <pre><code>EventParticipants ----------------- event_id user_id group_id </code></pre> <p>and allow the values of user_id and group_id to be NULL if that record is dealing with the other type of information.</p> <p>Of course, I could just break EventUsers and we'll call it EventGroups into 2 different tables but I'd like to keep who is tied to an event stored in one single place if there's a good logical way to do it.</p> <p>So, am I overlooking a good way to accomplish this?</p>
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    1. COYou could have an "EventGroups" table for `event_id, group_id`. A single user could be in a group that contains only that user. At least that feels a bit cleaner in some ways.
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