Is it good practice to use the email address as the primary key in many tables in the website system?

Question

For example, a website like stackoverflow.com, is it useful to use an email address to identify users in many tables?

It’s bad if the primary key is very long, say

VARCHAR (50)

or even

VARCHAR (100)

?

Answer 1

Not really. For any significant data set, you end up wasting a lot of space, and when polling you will get a performance hit. Also, if someone modifies their email (which you may or may not allow), you need to change it everywhere.

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Answer 2

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Answer 3

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Answer 4

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Answer 5

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Answer 6

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If your columns are indexed correctly, most modern databases (Oracle, Postgres, SQLServer) will not punish you for participating in an email address. If you are worried about joins, create a denormalized materialized view and pay the price for insert / update.