Model a Zero or One to Many Relationship

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Published on 2010-03-27T17:27:23Z Indexed on 2010/03/27 17:33 UTC
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How should I model a zero or one to a many relationship in the database? For example, a user record may or may not have a parent. So should my user table have a t_user.parent_id or should I have an associative table called t_user_hierarchy with the columns t_user_hierarchy.parent_id and t_user_hierarchy.user_id?

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