title: How to join two large tables with different strings
body: <p>I have two tables </p>
  
  <pre><code>table1
  customer_id 
  101
  102
  103 
  </code></pre>
  
  <p>and table2 </p>
  
  <pre><code>customer_id country_id 
    AO-101      1
    AO-102      2    
    AO-103      3
  </code></pre>
  
  <p>both the tables are very large tables I have used <code>CONCAT(table1.customer_id)</code> for joining with the table2</p>
  
  <p>all the fields stated above are index fields </p>
  
  <p>joining them and getting all the customer of country 1 is taking lot of time </p>
  
  <p>Can anyone help me please?</p>