AlterQuery  t_proj (children 3)
 ExpressionList (children 1)
  AlterCommand ADD_PROJECTION (children 1)
   Projection (children 1)
    ProjectionSelectQuery (children 1)
     ExpressionList (children 3)
      Function avg (children 1)
       ExpressionList (children 1)
        Identifier a
      Function avg (children 1)
       ExpressionList (children 1)
        Identifier b
      Function count (children 1)
       ExpressionList
 Identifier t_proj
 Set
