title: how mysql handle multiple START TRANSACTION (nesting?)
body: <p>I can't find the answer : how MySQL handle when in the same connection I call multiple time START TRANSACTION</p>
  
  <p>for example does the autocommit the current one in order to start a fresh new or does he nest them?</p>
  
  <p>NB : this is not a duplicate of <a href="https://stackoverflow.com/questions/1306869/are-nested-transactions-allowed-in-mysql">Are nested transactions allowed in MySQL?</a> because I don't whant to know if mysql allow it, or how to simulate this behaviou. I found that mysql does not nest the  transactions and I want to know how MySQL actually handle nested START TRANSACTION (by commiting the old one, by ignoring the new start transaction, ...)</p>