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lynda
Starting Member
21 Posts |
 Posted - 2009-06-29 : 14:04:07
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| In the database that I use, there are tables like:UserProductTypeUserIn USER there is a PK identity column called ID.In ProductTypeUser the PK is also ID, not identity and is FK to the PK in USER.What is the advantage of this? Is this a better design than having a typical ID int identity column as the PK and a seperate FK column that relates back to the PK in USER?Thanks much!Mike |
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TG
Master Smack Fu Yak Hacker
6065 Posts |
Posted - 2009-06-29 : 14:26:55
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| That would indicate that it is a one-to-(zero or one) relationship. So you cant have more than one ProductType per userID. ProductTypeUser becomes kind of an extension to the [USER] table. The advantage could be to sort of partition the data between the two tables making two narrower tables rather than t wide table. A possible reason to seperate the tables is if you have many Users that don't have any productType info.Be One with the OptimizerTG |
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lynda
Starting Member
21 Posts |
Posted - 2009-06-29 : 14:52:07
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| Ahh excellent, that makes total sense since indeed, there will be a subset of records in ProductTypeUser of those records in USER (so indeed a one-to-(zero or one) exists).Thanks! |
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PK is FK too?