Hi, Andreas,
My fault. You are absolutely right that tab.h was in error. Your
patch has been applied. I am adding a small test for this problem and
then check the update code into the SVN repository. Thanks.
John
On 3/3/2010 11:29 AM, Andreas Streichardt wrote:
> On Wednesday 03 March 2010 20:12:51 K. John Wu wrote:
>> Hi, Andreas,
>
> Hi John,
>
>> Here is how I understand the SQL standard,
>>
>> select count(*) ...
>>
>> should return a table with one row and one column, and the content of
>> the single value should be the value of "count(*)". So if you ask how
>> many rows the table object has, it should return 1, similarly for the
>> number of columns. One needs to get the actual content of the table
>> to find out how many rows satisfy the query conditions.
>
> COUNT(*) tells us how many rows the result set (table) has.
>
> Short example in mysql:
>
> mysql> SELECT COUNT(*) FROM login_att;
> +----------+
> | COUNT(*) |
> +----------+
> | 7 |
> +----------+
>
> On the other hand:
>
> mysql> SELECT COUNT(login_expire) FROM login_att;
> +---------------------+
> | COUNT(login_expire) |
> +---------------------+
> | 2 |
> +---------------------+
>
> This counts all NON NULL values of the specified field in the table.
>
> What fastbit currently does (without my patch): It always reports 1 as
> COUNT(*) which is definately wrong here.
>
>> I guess what you want might be a tabula object. To get that one,
>> leave the select clause a blank string or a nil pointer. Since I did
>> not see anything in SQL standard about a missing select clause, I have
>> implementation a table with a certain number of rows but without
>> columns -- a fairly silly object, but might be what you are after.
>
> What i am currently doing is i am faciliating the table::select interface of
> fastbit. This creates a tabele object for count(*) and this one currently
> reports 1 for every COUNT(*) query. So i am not using the lower level stuff of
> fastbit yet.
>
> These are the lines in mensa.cpp:
>
> else if (stricmp(sel, "count(*)") == 0) { // count(*)
> int64_t nhits = computeHits(cond);
> if (nhits< 0) {
> return 0;
> }
> else {
> std::string des = name_;
> if (! desc_.empty()) {
> des += " -- ";
> des += desc_;
> }
> return new ibis::tabele(cond, des.c_str(), nhits);
> }
> }
>
> Here fastbit correctly counts the number of hits and creates a correct tabele
> object.
>
> After selecting via table::select i am generating a cursor:
>
> ibis::table::cursor *cur;
> cur=result->createCursor();
> while (0 == cur->fetch()) {
> [...]
> else if (tps[j]==ibis::ULONG)
> {
> uint64_t ivalue;
> cur->getColumnAsULong(nms[j],ivalue);
> }
> [...]
>
> Here i am always getting a 1 due to the problem in the cursor.
>
> Am i doing something wrong here? If not i am pretty sure i hit a bug :S
>
>> If anyone knows exactly what the SQL standard intended, please let us
>> know.
>
> I am not really into the SQL standard but i am pretty sure that the mysql
> behaviour is as intended by the standard here.
>
>> John
>
> Kind regards,
>
> Andreas Streichardt
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