title: Combining 2 tables- Subquery returns more than 1 row
body: <p>When i join 2 tables i am getting an error</p>
  
  <pre><code>select * from picture where id=(SELECT id FROM user where age= 40 ) 
  </code></pre>
  
  <blockquote>
    <p>#1242 - Subquery returns more than 1 row</p>
  </blockquote>
  
  <p>What is the best way to join these 2 large data tables? I want to have all the results</p>