Should I use a unique string as a primary key, or should I use it as a separate INT auto-increment?

Question

Possible duplicates:
Surrogate Vs. Natural / Business Keys
When not to use surrogate primary keys?

So, I would prefer to have INT as a primary key with AI. But, here is the reason why I am considering making a unique string as a primary key :. I should not query related tables to retrieve the primary key, since I already know it

For example:
I have a lot of relationships:

Customer - Order - Product

Let's say I want to add a new customer and a new order, and I already know what they bought. I have to query the product table to get an INT, but if I have a string (unique) that is the primary key I shouldn't make a query (this seems cleaner than me, I'm not talking about optimization / runtime, not at all )

Answer 1

If you do not care about optimization, the main 2 criteria for the primary key are:

• Uniqueness

• Constant (never changes)

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Answer 2

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Answer 3

Er...

• Your logical model and design will use a unique string. This is a natural key.
• Actual implementation may use numeric automatic column number (surrogate key) due to architecture / performance