Ok, Eliot is partially correct.
If the "Inquiry_Email" is an attribute of the USER then it needs to be in the Users table. If it's an attribute of the Link (each link a user has may have a different Inquiry_Email address), then it's ok to store in the Link record. What you want to do is "seed" the database with the existing information, but allow it to be changed on a link by link basis, then you can do it.
This is not an easy thing to do with SQL, since you'd need to join the Links records to the Users records on the Username field, then update Links.Inquiry_Email with the Users.Email field. It's easy to have a complex query like this go awry, if it's possible to do at all the way you want it (MySQL is not a very robust complex query language, it's design is to be simple and straight forward).
It would be safer to do it as a short script, that would read through the users table, and update all links for that user.
If you don't have many links, your script could do it by starting out by selecting DISTINCT Username from Links, then iterating through that list -- only users who have links would be checked. If you have a lot of links, you'd need to do it in stages. But, I've found it to be often times better to do it "safely" than issue a query that does a scramble on you your database.
You might want to re-think this in light of the Contact_Email field being added back in as a default field.
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