title: MySQL left join query too slow
body: <p>I'm using this SQL query to join two tables and it takes 10 seconds even with a limit of 10. I've checked if the tables are indexed and they are so I'm out of ideas. Any help will be appreciated.</p>
  
  <pre><code>SELECT * FROM client_registration_request
  LEFT JOIN customers ON (client_registration_request.customer_reference=customers.reference) 
  LEFT JOIN region_info ON ( customers.country = region_info.id ) 
  WHERE client_registration_request.client = 23
  LIMIT 10
  </code></pre>
  
  <p>Here are the results from explain select</p>
  
  <p><img src="https://i.stack.imgur.com/ER50E.jpg" alt="explain select"></p>
  
  <p>client_registration_request index</p>
  
  <p><img src="https://i.stack.imgur.com/eAEhn.jpg" alt="client_registration_request index"></p>
  
  <p>customers index </p>
  
  <p><img src="https://i.stack.imgur.com/vOVYE.jpg" alt="customers index "></p>
  
  <p>and region_info index
  <img src="https://i.stack.imgur.com/K0ycV.jpg" alt="and region_info index"></p>