SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 4)
    Identifier a1
    Identifier a2
    Identifier tab1.b1
    Identifier tab2.b2
   TablesInSelectQuery (children 2)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier tab1 (alias first)
    TablesInSelectQueryElement (children 2)
     TableExpression (children 1)
      TableIdentifier tab2 (alias second_)
     TableJoin (children 1)
      Function equals (children 1)
       ExpressionList (children 2)
        Identifier b1
        Identifier a2