title: Flutter sqflite open existing database
body: <p>How can open existing db from assets with flutter and sqflite? 
  I read this guide : 
  <a href="https://github.com/tekartik/sqflite/blob/master/doc/opening_db.md#preloading-data" rel="noreferrer">https://github.com/tekartik/sqflite/blob/master/doc/opening_db.md#preloading-data</a></p>
  
  <p>But my app shows 'not found table' error
  Thanks.</p>