title: How to use GROUP BY to concat strings in mysql
body: <p>normal query</p>
  
  <pre><code>id  sid  string
  5    1    AAA
  6    1    BBB
  7    2    CCC
  8    3    ZZZ
  9    3    EEE
  </code></pre>
  
  <p>i want</p>
  
  <pre><code>sid  string
  1    1. AAA 2. BBB
  2    1. CCC
  3    1. ZZZ 2. EEE
  </code></pre>
  
  <p>Do you have any idea how to do?</p>