title: Define name for column func.count in sqlalchemy
body: <p>There are two tables
  </p>
  
  <pre><code>Tbl1 = Table(
      'tbl_1', metadata,
      Column('id', Integer, primary_key=True),
      Column('user_id', Integer, ForeignKey('user.id'), nullable=False),
      ...other columns
  )
  </code></pre>
  
  <p>and
  </p>
  
  <pre><code>Tbl2 = Table(
      'tbl_2', metadata,
      Column('id', Integer, primary_key=True),
      Column('user_id', Integer, ForeignKey('user.id'), nullable=False),
      ...other columns
  )
  </code></pre>
  
  <p>I want to count all data in both tables for one user.</p>
  
  
  
  <pre><code>q1 = Tbl1.count().where(Tbl1.c.user_id == some_id)
  q2 = Tbl2.count().where(Tbl2.c.user_id == some_id)
  union = q1.union(q2).alias('uni')
  query = sqlalchemy.select([sqlalchemy.func.sum(union.c.tbl_row_count)], from_obj=union)
  </code></pre>
  
  <p>And question is - how to set a column name for union count column, instead of looking thrue the internals? <em>union.c.tbl_row_count</em> i saw only in debug mode.</p>
  
  <p>Second try was:
  </p>
  
  <pre><code>import sqlalchemy as sa
  
  q1 = sa.select([sa.func.count(Tbl1.c.id).alias('cnt')]).where(Tbl1.c.user_id == some_id)
  q2 = sa.select([sa.func.count(Tbl2.c.id).alias('cnt')]).where(Tbl2.c.user_id == some_id)
  union = q1.union(q2).alias('uni')
  </code></pre>
  
  <p>But in that case internal name for column was <em>uni.c.count_1</em></p>