title: python sqlalchemy, get only one column problem
body: <p>Hello I want to get only one query column using only <code>Table.select()</code>, but I am having a problem</p>
  <pre class="lang-py prettyprint-override"><code>guild_id= 807887608943738881
  guild = meta_data.tables['guild_'+str(guild_id)] 
  
  a= engine.execute(guild.select([guild.c.age]).where(guild.c.user_id== user_id)).fetchall()
  print(a)
  </code></pre>
  <p>This code returns this</p>
  <pre><code>sqlalchemy.exc.ArgumentError: SQL expression for WHERE/HAVING role expected, got [Column('age', INTEGER(display_width=11), table=&lt;guild_807887608943738881&gt;)].
  </code></pre>
  <p>What's wrong with the <code>age</code> column?</p>