No you can not do that. In case of table column types,the capital letters that are given by meta like "I", "C" ,"J" etc are not an actual datatype in kdb. They are just used to represent general list with some additional characteristics in case of tables. So if you want to convert empty list () to "C" (or "I"), basically its the conversion from general list to general list. Its only after first record you can get "C" but again kdb doesn't stops you from inserting any other type of data later in that column as also mentioned in other post.