It is not redundant, not having a primary key keeps the door closed to a lot of things. Even for basic functions, the database works off of an indexed primary key much faster than a varchar value floating in a tables values.

Expansibility wise it is also a good idea. Primary keys make everything easy and fast to reference, you can also change anything else on the row without a problem.

Once again, its simply good practice to put a primary key in. Now it is not required, but being able to run does not make an application good.

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