title: Default values for varchar and int mysql data types
body: <p>The screenshot show 3 typical definitions of data type: id (autoincrement), a title and a number.</p>
  
  <p>1.- Which are differences between: <code>none</code> and <code>NULL</code>?<br>
  2.- Do I must choose <code>as defined: ''</code> for varchar types when I want an empty string?<br>
  3.- Do I must put an <code>as defined: 0</code> default value for autoincrement int types?</p>
  
  <p><img src="https://i.stack.imgur.com/KR83F.png" alt="enter image description here"></p>