SelectWithUnionQuery (children 1)
 ExpressionList (children 1)
  SelectQuery (children 2)
   ExpressionList (children 1)
    Function concatWithSeparator (children 1)
     ExpressionList (children 3)
      Literal \'a\'
      Identifier c1
      Literal \'b\'
   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 c1) (children 1)
            ExpressionList (children 2)
             Literal UInt64_1
             Literal \'Nullable(UInt8)\'
