Hi, Dominique,
The intention was to not have NULL values in the results. The query
answering function take into account of the null masks to eliminate
NULL values. Internally, strings are represented as std::string. The
constructor can not usually take a nil pointer. The particular error
might due to this problem with passing a nil to std::string
constructor. Anyway, there might be an issue if we have a NULL in the
answer set. It could be worthwhile to look into this further.
The problem with NULL string values is that all three forms you've
suggested could be valid string values. Presumably, we could settle
on one, say the empty string "". This might be the most reasonable
choice as the CSV reader actually will treat empty strings as NULL
values. This probably means that other database systems output empty
strings for NULL values.
John
On 1/24/12 12:40 PM, Dominique Prunier wrote:
> Hmm, just discovered something bad with the patch. If the key is 0
> (which means NULL), the new ibis::category::selectStrings fails
> with "basic_string::_S_construct NULL not valid". The is no clear
> convention for what is a null string in FastBit interfaces ("",
> NULL, "<NULL>") but i guess an empty string would be the best fit
> here, right ?
>
> Thanks,
>
>
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