From: Wade Maxfield
Date: March 16 1999 4:49am
Subject: Re: Info about retrieving in C api. Possible bug?
List-Archive: http://lists.mysql.com/mysql/303
Message-Id: <Pine.LNX.4.04.9903152243360.9564-100000@one.ctelcom.net>
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On Mon, 15 Mar 1999, Paul DuBois wrote:

> At 10:24 PM -0600 3/15/1999, Wade Maxfield wrote:
> >  OK. I've got compile and link with mysql.  I connected to the database.
> >
> >  if you use mysql_affected_rows(&mysql) after a select, it returns a
> >non-zero value even if 0 rows were returned.
> >
> >  You actually have to try to fetch the row before you find out no data
> >was selected.  The documentation says you find the number of rows
> >retrieved by the select.  I think this is a bug.
> 
> It depends, and it's difficult to say without seeing your code.  However,
> if you're using mysql_use_result() as you describe below, it's not a
> bug, for the reason given below.


"  Returns the number of rows affected by the last UPDATE, DELETE or
INSERT
query. May be called immediately after
mysql_query() for UPDATE, DELETE or INSERT statements. For SELECT
statements, mysql_affected_rows()
works like mysql_num_rows(). "

  I read the documentation wrong. I _assumed_ it could always be called
immediately after mysql_query() for a select call, since I did not parse
the words carefully enough.




> 
> I'm curious; is there something in the manual that led you to expect
> you'd be able to get the row count with mysql_use_result() without
> fetching the rows?  If so, that needs to be fixed.


  Not exactly.  I read this :
"The use of mysql_num_rows() depends on whether you use
mysql_store_result() or mysql_use_result() to
return the result set. If you use mysql_store_result(), mysql_num_rows()
may be called immediately. If you use
mysql_use_result(), mysql_num_rows() will not return the correct value
until all the rows in the result set have been
retrieved. "

  I did not expect an exact number of rows to be returned.  I did expect 0
or non-zero, where 0 would key me to skip trying to do anything.

  I found out later that even with 0 rows, you must call mysql_fetch_row()
to get the system to settle down.  OH, well.

  Other than that, it worked like a charm.

wade