Databases
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POOne to Many Database Relationship
 

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    <p>Guys I would really appreciate it if someone could help me with this. I have a schema with 4 tables relevant to this question Books, Groups, ReadingList, Comments. A user of the system can join a group and add books to that group's reading list. A group's book list is represented by the table ReadingList:</p> <pre><code>ReadingList ------------- Id (auto_increment) ReadingListID BookID (pk) GroupID (pk) </code></pre> <p>BookID and GroupID are set up as a composite primary key to ensure no book can appear on a groups reading list twice. Both these fields have a fk defined to the relevant table Books/Groups. Now my problem comes when trying to set up a relationship between the Comments table and the ReadingList. The theory is that each unique entry in the ReadingList can have many comments (1..*) so basically one book on a groups reading list can have many comments associated with in. The Comments table looks like this:</p> <pre><code>Comments ----------- Id (pk, auto_increment) ReadingListID UserName Comment TimeStamp </code></pre> <p>My logic is that a fk be set up from Comments (ReadingListID) to ReadingList (ReadingListID) but I am clearly flawed as I get a 'no primary or candidate keys in referenced table' error.</p> <p>I have tried a variety of things like making ReadingListID &amp; Id in the Comments table a composite key and making ReadingListID a pk in the ReadingList table etc, but I just can't get my head round this. Please let me know if I haven't been clear enough.</p> <p>Many thanks!</p>
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    1. COHow do you create ReadingList-> ReadingListID and is it unique?
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A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

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