I did a "DELETE FROM picture" where "picture" is a table in my database.

Afterward, this piece of code does not generate an error
----------------------------------------------
try
{
$query = "SELECT * FROM picture p " .
"WHERE p.pictureFile='" . $pictureFile . "'";
$thisRow =
mysql_query($query, $pictures_connection);
}
catch(Exception $e)
{
echo 'caught exception: ', $e->getMessage()."\n";
$result = False;
}
----------------------------------------------
and testing $thisRow
----------------------------------------------
if(!$thisRow)
{
echo "picture '" . $pictureFile . "' does not exist in the
database.\n";
}
else
{
echo "picture '" . $pictureFile . "' exists in the database.\n";
$picture_table = array();
$picture_row = mysql_fetch_array($thisRow);
do /* capture row's picture data */
{
$picture_table[$picture_row["pictureHandle"]] = array(
"pictureName" => $picture_row["pictureName"],
"pictureFile" => $picture_row["pictureFile"],
"pictureMapFile" => $picture_row["pictureMapFile"],
"pictureDescription" => $picture_row["pictureDescription"],
"pictureDescriptionFile" =>
$picture_row["pictureDescriptionFile"],
"pictureDateTime" => $picture_row["pictureDateTime"],
"pictureOrientation" => $picture_row["pictureOrientation"],
"pictureStamp" => $picture_row["pictureStamp"]

) /* add this row to the table */;
} while(($picture_row = mysql_fetch_array($thisRow)));
print_r($picture_table) . "\n";
------------------------------------------------------------ ----
results in an empty array being printed ... implying that the query
was successful?

Help, please.



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Stan wrote:
> I did a "DELETE FROM picture" where "picture" is a table in my database.

Because this deletes all your records - so doing a select afterwards
will find nothing.

> Afterward, this piece of code does not generate an error
> ----------------------------------------------
> try
> {
> $query = "SELECT * FROM picture p " .
> "WHERE p.pictureFile='" . $pictureFile . "'";
> $thisRow =
> mysql_query($query, $pictures_connection);
> }
> catch(Exception $e)
> {
> echo 'caught exception: ', $e->getMessage()."\n";
> $result = False;
> }

an empty result set is fine - it means no records found. It will not
generate an exception.

I'm not sure when mysql will generate an exception either, mysql_query
returns FALSE if the query fails (see http://www.php.net/mysql_query).
You then have to use mysql_error to get the reason why it failed.

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Yes. I deleted all records.

Prior to the DELETE, if I did a SELECT with specific criteria (WHERE
p.pictureFile = "some valid content"), and those criteria were not met,
mysql_query() returned False ... and, conversely, if those criteria were
met, mysql_query() returned "a resource" against which I could use
mysql_fetch() to retrieve the rows returned by the SELECT.

After the DELETE, and as I explained in my original post, the same SELECT
with specific criteria returns, not False as it should, but "a resource"
which contains an empty row.

If I look at the database using MySQL Query Browser, it appears empty.

I do not understand what is happening.

Help understanding what is happening is what I seek. Can you help?

Thanks.


"Chris" <dmagick [at] gmail.com> wrote in message
news:4AAD74E5.3090505 [at] gmail.com...
> Stan wrote:
> > I did a "DELETE FROM picture" where "picture" is a table in my database.
>
> Because this deletes all your records - so doing a select afterwards
> will find nothing.
>
> > Afterward, this piece of code does not generate an error
> > ----------------------------------------------
> > try
> > {
> > $query = "SELECT * FROM picture p " .
> > "WHERE p.pictureFile='" . $pictureFile . "'";
> > $thisRow =
> > mysql_query($query, $pictures_connection);
> > }
> > catch(Exception $e)
> > {
> > echo 'caught exception: ', $e->getMessage()."\n";
> > $result = False;
> > }
>
> an empty result set is fine - it means no records found. It will not
> generate an exception.
>
> I'm not sure when mysql will generate an exception either, mysql_query
> returns FALSE if the query fails (see http://www.php.net/mysql_query).
> You then have to use mysql_error to get the reason why it failed.
>
> --
> Postgresql & php tutorials
> http://www.designmagick.com/
>



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OK.

If I change the test to "if(mysql_num_rows($thisRow) < 1)" it does what I
want.

I guess if I want to understand why False was returned originally (just
after I created the database) I need to start over.

Do I have 4 possible conditions here: 1) the mysql_query() function fails
and I get a PHP error, 2) the query fails at the server and I get False, or
3) the query doesn't fail at the server and I get "a result" that a) is
empty, or b) contains 1 or more rows? Yes.

Problem solved (my code was naive), understanding increased (my code won't
be naive in the future as regards mysql functions in PHP).

Thank you very much..

"Chris" <dmagick [at] gmail.com> wrote in message
news:4AAD74E5.3090505 [at] gmail.com...
> Stan wrote:
> > I did a "DELETE FROM picture" where "picture" is a table in my database.
>
> Because this deletes all your records - so doing a select afterwards
> will find nothing.
>
> > Afterward, this piece of code does not generate an error
> > ----------------------------------------------
> > try
> > {
> > $query = "SELECT * FROM picture p " .
> > "WHERE p.pictureFile='" . $pictureFile . "'";
> > $thisRow =
> > mysql_query($query, $pictures_connection);
> > }
> > catch(Exception $e)
> > {
> > echo 'caught exception: ', $e->getMessage()."\n";
> > $result = False;
> > }
>
> an empty result set is fine - it means no records found. It will not
> generate an exception.
>
> I'm not sure when mysql will generate an exception either, mysql_query
> returns FALSE if the query fails (see http://www.php.net/mysql_query).
> You then have to use mysql_error to get the reason why it failed.
>
> --
> Postgresql & php tutorials
> http://www.designmagick.com/
>



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Stan wrote:
> OK.
>
> If I change the test to "if(mysql_num_rows($thisRow) < 1)" it does what I
> want.
>
> I guess if I want to understand why False was returned originally (just
> after I created the database) I need to start over.

According to the docs mysql_query only returns false if there's an error.

> Do I have 4 possible conditions here: 1) the mysql_query() function fails
> and I get a PHP error, 2) the query fails at the server and I get False, or
> 3) the query doesn't fail at the server and I get "a result" that a) is
> empty, or b) contains 1 or more rows? Yes.

1) I'm not sure what you mean. If you try to run a query before having a
connection (or not checking the connection is valid before running a
query), then mysql_query will return false and php will throw warnings
or notices (can't remember which).

2) Correct

3) Also correct.

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