[NTLUG:Discuss] Decipher C++ source

[Fred James]

Michael Barnes wrote:
> I have a MySQL database that logs telephone calls.  A module puts the
> CallerID number into a variable.  Then, this database query is
> supposed to return the last date and time that number called.  The
> database table has fields for NUMBER, NAME, CALL_DATE and CALL_TIME.
> (There are others, but I don't care about them for this purpose.)
>
> Anyhow, it appears that the query is giving me the first time the
> number called, not the latest time.
>
> I'm hoping some good programmer out there could take a peek at this
> and answer some questions.
> First I need to know why I get the first call instead of the last call.
> Then some curiosity questions.
> What is the significance of the '!' after the NAME field?
> Is the value \"\"  for NAME some type of a variable or wildcard?
>
> What line(s) actually select the proper data (last call) from the list
> returned by the query?
>
> Once it gets the right data, it puts it into an element in the
> BusDriver module.  It also increments the call counter, which is
> working correctly.
>
> Here's the code.
>
>   sql=QString().sprintf("select CALL_DATE,CALL_TIME from DETAILS_GAL \
>                          where (NUMBER=\"%s\")&&(NAME!=\"\") \
>                          order by CALL_DATE,CALL_TIME desc",
> 			(const char *)mon->showCode(),
> 			(const char *)pnum);
>   q=new QSqlQuery(sql);
>   if(q->first()) {
>     mon->metaData(line)->
>       setElement(BusDriver::LastCallDatetimeElement,
> 		 QString().sprintf("%d",QDateTime(q->value(0).toDate(),
> 						  q->value(1).toTime()).
> 				   toTime_t()));
>   }
>   mon->metaData(line)->setElement(BusDriver::CounterElement,q->size());
>   delete q;
>
>
> Any comments, English translations/explanations, potential problems,
> etc. are appreciated.
>
> Thanks,
> Michael
>   
Michael Barnes
At first glance, the issue is in the embedded SQL statement ... 
specifically the 'order by' clause ...
    The 'desc' (descending) applies only to CALL_TIME?
    Should read something like
       order by CALL_DATE desc, CALL_TIME desc
For Reference, See 
<http://dev.mysql.com/doc/refman/5.0/en/sorting-rows.html>
Hope that helps
Regards
Fred James