我应该使用用户的md5密码通过电子邮件验证他的帐户吗？

I am creating a register form and I will have an email verification. The email will have an activation link that will update verified column from 0 to 1. Since the user's password is hashed with md5 I thought instead of creating a new column with a random number to use as verification, I thought to use his password.

So instead of *domain.com/verification.php?token=new_random_number* I will have domain.com/verification.php?token=md5

How do you find this ?

This is of course just to avoid one column.

Generate a new random ID for the explicit purpose of the email, then you can invalidate/clear the ID after the user has performed the account management action.

you can use something like :
$secret_word ='COMPLEX-WORD-HERE';
$validation_token = substr(md5($user_password.$secret_word),0,10); I highly recommend using username instead, since it's unique per user
101% secure :)