SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 4)
    Identifier a1
    Identifier a2
    Identifier first.b1
    Identifier second_.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