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Comments on What are the pros and cons of a composite primary key versus a unique constraint?

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What are the pros and cons of a composite primary key versus a unique constraint?

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Let's say we have two tables A and B and a join table C that has foreign keys to both A and B and the combination of those foreign keys is unique.

One could either do a unique constraint or a composite primary key on those columns.

What would the pros and cons of either solution to this be?

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One could either do a unique constraint on those foreign keys or a composite primary key on those columns.

For elegance, canonicity, a primary key is necessary. You would initially have a primary key on those columns.

However, for sortability reasons, you would eventually use just a primary key on a single column ad-hoc created to be the id/key, so no, in the end you don't have a primary key on those columns, but a unique constraint.

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meriton‭ wrote over 3 years ago

What do you mean with "sortability reasons"? Also, Charlie said the combination of both columns is unique. That doesn't imply that a single colum is unique. That is, you can't create a primary key on a single column ...