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I do not have an index on the email field ... The way it works is that users have entered their email as their login.
So in order to authenticate each User (as they log in), you need to look up their email address. That means that each email address
must be unique, i.e. must identify a
single User.
It also means that you definitely
do need an index on email address, otherwise your log-in process is gong to get slower and slower (and slower) as the number of Users increases.
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I don't want them to have two of the same employee_emails because this will screw up the rest of the logic in the app.
And you've answered your own question - you
cannot have duplicate email addresses.