Quickest way to check for pre-existing record before insert [mysql_errno()]

Question

My question will use emails as an example, but this could apply to anything.

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Normally before registering a new user (including inserting his/her email) I check

Answer 1

I believe that COUNT is one of the quickest methods. Also remember when doing your queries, if you only want to test its existence don't do a

SELECT *

Instead specify a specific field

SELECT id

So you are not retrieving as much data. In the case of using COUNT:

SELECT COUNT(id) FROM Users WHERE email = 'emailaddress'

Please see below link on how to use COUNT in a result set

http://www.tizag.com/mysqlTutorial/mysqlcount.php

Answer 2

Use

INSERT IGNORE INTO Users VALUES(...);

with a unique key on email field, then check row count with mysql_affected_rows();

This will result in a single query to the DB and rule out the race condition of the time window between SELECT and INSERT