Question

I have the following Mysql select that returns all the duplicate email addresses in my table.

SELECT users.FirstName, `Surname`, users.email1
FROM users
INNER JOIN (  
    SELECT email1   
  FROM users
GROUP BY email1   
HAVING count(email1) > 1) dup ON users.email1 = dup.email1   
ORDER BY users.email1   

This works great, what I wish to do now is update a field called users.DupEmail with “YES” but I am unsure how to do this. I have tried putting an update line to replace the select, but I am clearly getting it wrong as I am back here asking for help.

Can anyone help please?

Answer 1

You can just use the multiple-table UPDATE syntax with a self-join:

UPDATE users AS u1
  JOIN users AS u2 USING (email1)
   SET u1.DupEmail = 'YES'
 WHERE NOT u1.id = u2.id; -- use your primary key here