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    <p>This concept should get you going:</p> <p><img src="https://i.stack.imgur.com/fblRq.png" alt="enter image description here"></p> <p>The user can see the product if:</p> <ul> <li>the corresponding row exists in USER_GROUP_PRODUCT</li> <li>or PRODUCT.PUBLIC is TRUE (and user is in at least one group, if I understand your question correctly).</li> </ul> <p>There are 2 key points to consider about this model:</p> <ol> <li>Liberal usage of <strong>identifying</strong> relationships - primary keys of parents are "migrated" within primary keys of children, which enables "merging" of GROUP_ID at the bottom USER_GROUP_PRODUCT. This is what allows the DBMS to enforce the constraint that both user and product have to belong to the <strong>same</strong> group to be mutually visible. Usage of <em>non-identifying</em> relationships and surrogate keys would prevent the DBMS from being able to enforce that directly (you'd have to write custom triggers).</li> <li>Usage of PRODUCT.PUBLIC - you'll have to treat this field as "magic" in your client code. The alternative is to simply fill the USER_GROUP_PRODUCT with all the possible combinations, but this approach is fragile in case a new user is added - it would not automatically see the product unless you update the USER_GROUP_PRODUCT as well, but how would you know you need to update it unless you have a field such as PRODUCT.PUBLIC? So if you can't avoid PRODUCT.PUBLIC anyway, why not treat it specially and save some storage space in the database?</li> </ol>
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    1. POHow should I record in the database that an item/product is visible by 'all' groups?
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    1. USBranko Dimitrijevic
    1. USBranko Dimitrijevic
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    1. COis the additional product field not simliar to that proposed by martin earlier, along with its special handling? and the `user_group_product` relation not essentially the final join in the query proposed by dems? not sure i'd have such a relation as a table, perhaps a view.
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      1. USpoop-deck
    2. CO@poop-deck In your question, you said: *"Users **can** see that item if they are in one of the assigned groups."*. I understood that as if users are **able but not required** to see it. If you need that kind of granularity, then you need USER_GROUP_PRODUCT to be a real table, not a view. If you don't, then this can be a view. BTW, yes PRIVATE looks equivalent to what Martin proposed.
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      1. USBranko Dimitrijevic
    3. COwow, "able but not required" would be pretty granular, but then again a user might choose items they wish to see regularly (as a subset of all those they are permitted to see). if so then it would seem a table is required. thx.
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