[wp-trac] [WordPress Trac] #33376: Create index on user_email and UNIQUE on user_nicename, user_email and user_login

[WordPress Trac]

#33376: Create index on user_email and UNIQUE on user_nicename, user_email and
user_login
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 Reporter:  chriscct7                     |       Owner:  chriscct7
     Type:  enhancement                   |      Status:  assigned
 Priority:  normal                        |   Milestone:  Future Release
Component:  Database                      |     Version:
 Severity:  normal                        |  Resolution:
 Keywords:  has-patch dev-feedback early  |     Focuses:  performance
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Comment (by DrewAPicture):

 Replying to [comment:3 chriscct7]:
 > Replying to [comment:2 knutsp]:
 > > This may fail for user_email, as a plugin could have allowed users
 with the same email.
 >
 > To do so would either require direct SQL calls or overriding tons of
 checks for email_exists in order to avoid the fact that WordPress prevents
 users from sharing an email address. I'm sure a plugin could be devised,
 if so desired, that could break on any nearly any change to WordPress
 core.
 >
 > A plugin that allows the same email to be shared would also break other
 issues like #9568 (login via an email address; which user gets logged in
 when they share an email?), as well as developers ability to count on
 predicable results to core functions like `get_user_by('email', $value)`.
 As such, changing the tables to not support duplicates simply complements
 checks WordPress already has.

 The [https://wordpress.org/plugins/allow-multiple-accounts/ Allow Multiple
 Accounts] plugin by @coffee2code has been a popular choice for years for
 allowing multiple accounts with the same email. So it's not really unheard
 of.

 And for what it's worth, it leverages the `pre_user_email` hook to do it.

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Ticket URL: <https://core.trac.wordpress.org/ticket/33376#comment:4>
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