title: MariaDB - How to add(JOIN) one more column from another table with IF/ELSE
body: <p>I've got two tables called <code>ARTICLE</code> and <code>SAVE</code>.</p>
  
  <p><code>ARTICLE</code> table has entire article data. And <code>SAVE</code> table has the relation between <code>email</code> and <code>seq</code> of <code>ARTICLE</code>.</p>
  
  <pre><code>ARTICLE
  seq email    title content
  1   fm@x.y   ya    hah
  2   ch@x.y   ho    hihi
  3   ch@x.y   yo    hoho
  
  SAVE
  seq email    article_seq
  3   ch@x.y   1
  </code></pre>
  
  <p>So, if you save the 3rd article with your account(<code>a@x.y</code>), <code>SAVE</code> table will be changed like...</p>
  
  <pre><code>SAVE
  seq email    article_seq
  3   ch@x.y   1
  4   a@x.y    3
  </code></pre>
  
  <p>And I'd like to create(The result of <code>SELECT</code>) one more column into ARTICLE call <code>is_saved</code>. And I expect this result of <code>SELECT</code>:</p>
  
  <p>When I log in as <code>ch@x.y</code></p>
  
  <pre><code>RESULT
  seq email    title content is_saved
  1   fm@x.y   ya    hah     1
  2   ch@x.y   ho    hihi    0
  3   ch@x.y   yo    hoho    0
  </code></pre>
  
  <p>When I log in as <code>fm@x.y</code></p>
  
  <pre><code>RESULT
  seq email    title content is_saved
  1   fm@x.y   ya    hah     0
  2   ch@x.y   ho    hihi    0
  3   ch@x.y   yo    hoho    0
  </code></pre>
  
  <p>So, I need to <code>JOIN</code> the two tables based on <code>ARTICLE</code> and I may need <code>IF/ELSE</code> condition. How can I do this?</p>