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sapator
Constraint Violating Yak Guru
462 Posts |
 Posted - 2009-10-10 : 17:10:00
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| Hi.This is just a curiosity question.I have seen some tables to have a FK relationship in one of their own columns.p.e. an id column with a relation on another column on the same table.Since i can't find anything solid on the net, can someone tell why and in what occasion this kind of relationship is useful?An example would be nice.Thanks. |
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webfred
Master Smack Fu Yak Hacker
8781 Posts |
Posted - 2009-10-10 : 18:13:37
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Think about employee and managers or set products and their childs. The are saved in the same table.Each entry has an ID and a referenceID to the ID that is NULL (if for example it is the manager himself) or a pointer to a parent.Do you know what I mean?
No, you're never too old to Yak'n'Roll if you're too young to die. |
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sapator
Constraint Violating Yak Guru
462 Posts |
Posted - 2009-10-10 : 22:23:40
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| Hi.Yes i think so, but what is better?To have a columns that says if it's a manager or not (0,1) or to have fk to the same table?And how will you find if it's a manager or not in a query?Won't you look for the value (of 0 or 1)?How will the fk to the same table help? |
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dportas
Yak Posting Veteran
53 Posts |
Posted - 2009-10-11 : 03:41:52
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quote:
Originally posted by sapator
Hi.Yes i think so, but what is better?To have a columns that says if it's a manager or not (0,1) or to have fk to the same table?And how will you find if it's a manager or not in a query?Won't you look for the value (of 0 or 1)?How will the fk to the same table help?
The point of the foreign key is that it tells you who the manager of each person is. In practice you would probably have another column to indicate a person's job title or seniority. |
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sapator
Constraint Violating Yak Guru
462 Posts |
Posted - 2009-10-11 : 19:02:44
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| Ah, ok made clearer to my mind.Thanks. |
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Reference same table question.