title: About unique=True and (unique=True, index=True) in sqlalchemy
body: <p>When I create tables use flask-sqlalchemy like this:</p>
  
  <pre><code>class Te(Model):
      __tablename__ = 'tt'
      id = Column(db.Integer(), primary_key=True)
      t1 = Column(db.String(80), unique=True, )
      t3 = Column(db.String(80), unique=True, index=True, )
  </code></pre>
  
  <p>and In my Sequel Pro , I get the table create info:</p>
  
  <pre><code>CREATE TABLE `tt` (
    `id` int(11) NOT NULL AUTO_INCREMENT,
    `t1` varchar(80) DEFAULT NULL,
    `t3` varchar(80) DEFAULT NULL,
    PRIMARY KEY (`id`),
    UNIQUE KEY `t1` (`t1`),
    UNIQUE KEY `ix_tt_t3` (`t3`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
  </code></pre>
  
  <p>this means t1 is entirely same as t3 in MySQL? So when you define <code>unique=True</code>, it's not require to define <code>index=True</code>?</p>
  
  <p>Thanks.</p>