title: Why is LEFT JOIN slower than INNER JOIN?
body: <p>I have two queries, the first one (inner join) is super fast, and the second one (left join) is super slow. How do I make the second query fast?</p>
  
  <pre><code>EXPLAIN SELECT saved.email FROM saved INNER JOIN finished ON finished.email = saved.email;
  
  id  select_type table   type    possible_keys   key key_len ref rows    Extra
  1   SIMPLE  finished    index   NULL    email   258 NULL    32168   Using index
  1   SIMPLE  saved   ref email   email   383 func    1   Using where; Using index
  
  EXPLAIN SELECT saved.email FROM saved LEFT JOIN finished ON finished.email = saved.email;
  
  id  select_type table   type    possible_keys   key key_len ref rows    Extra
  1   SIMPLE  saved   index   NULL    email   383 NULL    40971   Using index
  1   SIMPLE  finishedindex   NULL    email   258 NULL    32168   Using index
  </code></pre>
  
  <p>Edit: I have added table info for both tables down below. </p>
  
  <pre><code>CREATE TABLE `saved` (
    `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
    `slug` varchar(255) DEFAULT NULL,
    `email` varchar(127) NOT NULL,
    [omitted fields include varchar, text, longtext, int],
    PRIMARY KEY (`id`),
    KEY `slug` (`slug`),
    KEY `email` (`email`)
  ) ENGINE=MyISAM AUTO_INCREMENT=56329 DEFAULT CHARSET=utf8;
  
  CREATE TABLE `finished` (
    `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
    `slug` varchar(255) DEFAULT NULL,
    `submitted` int(11) DEFAULT NULL,
    `status` int(1) DEFAULT '0',
    `name` varchar(255) DEFAULT NULL,
    `email` varchar(255) DEFAULT NULL,
    [omitted fields include varchar, text, longtext, int],
    PRIMARY KEY (`id`),
    KEY `assigned_user_id` (`assigned_user_id`),
    KEY `event_id` (`event_id`),
    KEY `slug` (`slug`),
    KEY `email` (`email`),
    KEY `city_id` (`city_id`),
    KEY `status` (`status`),
    KEY `recommend` (`recommend`),
    KEY `pending_user_id` (`pending_user_id`),
    KEY `submitted` (`submitted`)
  ) ENGINE=MyISAM AUTO_INCREMENT=33063 DEFAULT CHARSET=latin1;
  </code></pre>