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