SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function concatWithSeparator (children 1)
     ExpressionList (children 3)
      Identifier c0
      Literal \'b\'
      Literal UInt64_1
   TablesInSelectQuery (children 1)
    TablesInSelectQueryElement (children 1)
     TableExpression (children 1)
      Subquery (alias tx) (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 1)
          ExpressionList (children 1)
           Function CAST (alias c0) (children 1)
            ExpressionList (children 2)
             Literal NULL
             Literal \'Nullable(String)\'
