I am using Sql Server for Visual Studio. I Have two columns, 1 is auto-incremented and the other is not but I want make the both primary keys and the unincremented key can be used as a foreign key in another table. thanks
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4As you describe it it makes zero sense. – TomTom Apr 11 '14 at 10:09
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Do you want a *composite* key, or do you want two *separate* keys? – Damien_The_Unbeliever Apr 11 '14 at 10:18
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Like TomTom said, what are you trying to do has no sense. If the second column (the one you are calling unincremented) is already unique, you can drop the auto-increment column because it's redundant and useless.
The redundancy is caused by the fact that 2 unique columns, aggregated in one single key, not only compromises the uniqueness of the columns themselves, but it uses 2 different columns to describe the same values!
id | col | some_data
-------------------------------
1 | A |
2 | B |
3 | D |
As you can see, if i want to point to a specific row, in this case you're describing, I can just use id or col columns and both of them are valid!
If instead, the unincremented column is not unique, the primary key should only be the auto-incremented column and this one should be used as foreign key in other tables.
The last option you have, if you really want to have 2 distinct columns, is to not set the first one as auto-increment column.
As a general rule auto-increment columns should always be used as a single-column key.
mordack550
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