SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 2)
    Identifier a1
    Identifier b1
   TablesInSelectQuery (children 2)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      TableIdentifier tab1
    TablesInSelectQueryElement (children 2)
     TableExpression (children 1)
      Subquery (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 or (children 1)
       ExpressionList (children 2)
        Function equals (children 1)
         ExpressionList (children 2)
          Identifier b1
          Identifier a2
        Function equals (children 1)
         ExpressionList (children 2)
          Identifier b2
          Identifier a1
