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POselecting based on all conditions being met (relational division)
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copied!<p>I have the tables question, topic and question_has_topic (many-to-many relationship). In my application admins see a breakdown for questions grouped by their topics and they select how many from each they'd like the system to randomly select to create a test.<br/> This is the kind of table they see:</p> <pre> +-----------------------+---------------------+------------+ | Topics | Questions available | Selection: | +-----------------------+---------------------+------------+ | health,safety,general | 13 | | | health | 3 | | | safety | 7 | | | general | 1 | | +-----------------------+---------------------+------------+ </pre> <p>The count is unique for the particular grouping of topics. Anyway, once they make the selection I need a SQL statement which will select questions that correspond to the given grouping of topics. I.e. I might need 3 questions which have the topics health,safety and general.<br/> I was doing some research online and I think that what I'm trying to do is known as divide in relational algebra and here is my attempt for an arbitrary grouping of topicids:</p> <pre> select questionid from question_has_topic where not exists ( select questionid from question_has_topic where topicid not in (8,9,10)) </pre> <p>The result is empty, although there are 2 questions in the database that have all these topic ids which tells me this isn't working. I was following the example from this <a href="http://luhong.wordpress.com/2006/03/05/relational-division-in-sql/" rel="nofollow">link</a></p>

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