[Resolved] [Resolved] The nasty "do-while" statement-just can't get rid of it.

mellow

I was reading a tutorial on zend.com on programming mistakes. It talks about using mysql_num_row to check for results instead of mysql_fetch_row(or _array). One of the benefits being that you did not need the "do" statement now because you do not fetch the first result when checking.

I have not found this to be so. in incorporating this into a script I am still missing the first result. If I use "do" I get all the results. Is there something wrong with using "the nasty do-while loop"?

laserlight

What the article probably meant was this:
If you attempt to get the first result set, then the result pointer is moved down by 1 row.
Now, you can verify that there is a first result set, but you already have it.
So, for looping purposes, you use a do while loop.
If you use a while loop, then your loop will miss the first result set, since the result pointer no longer points there.

On the other hand, by finding the number of rows returned by the query, the result pointer isnt moved at all (or maybe is moved, but then reset).
This means that using a while loop will include the first result set, as required.
This can be considered cleaner than using a do while loop, since the reader has to read all the way down to view the loop condition, which can be troublesome if the code in between is substantial.

To apply this to your problem, it means that although you have incorporated mysql_num_rows(), you still have the extra mysql_fetch_* that is moving your result pointer by 1 row.

mellow

Here is the code I am using. This code skips the first result. Even though I am checking with num_rows, I do not have the fetch_array in until after the while loop starts--so I would think the pointer would would still be at result 0. I guess it is not a big deal but I am trying to understand what is going on here. Thanks for your time in replying.

$results = mysql_query($sql);
$rows = mysql_fetch_array($results);
if (mysql_num_rows($results) < 1){
echo "There are no units like this available at this time.";
exit;
}
//should display for riders or walks

if (1 | 2 == $query){
echo "<table border=1>\n";
echo "<tr>\n";
echo "<td>More Info</td><td>Year</td><td>Brand</td><td>Model</td><td>HP</td><td>Cut</td><td>Price</td>\n";

while ($rows = mysql_fetch_array($results)){
printf("<tr><td><a href=\"%s?id=%s\">%s</a></td><td>%s</td><td>%s</td><td>%s</td><td>%s</td><td>%s</td><td>%s</td></tr>\n",$PHP_SELF, $rows["id"],$rows["id"],$rows["year"],$rows["brand"],$rows["model"],$rows["hp"],$rows["cut"],$rows["price"]);
}//closes while statement
echo "</table>\n";
}//closes if statement

laserlight

I do not have the fetch_array in until after the while loop starts

$results = mysql_query($sql);
$rows = mysql_fetch_array($results);

hmm... somehow that line in bold looks vaguely familiar.... 😃

mellow

My understanding(which may be minimal) is that the row
$rows = mysql_fetch_array($results) only set the value of the variable $rows and did not actually fetch anything at that point.

But that must not be correct?

laserlight

There's this thing called the PHP Manual, which can be found at php.net
Let's have a look at the entry for [man]mysql_fetch_array/man

(PHP 3, PHP 4 )
mysql_fetch_array -- Fetch a result row as an associative array, a numeric array, or both.
Description
array mysql_fetch_array ( resource result [, int result_type])

Returns an array that corresponds to the fetched row, or FALSE if there are no more rows.

Also, what you said about setting the value of $rows only does not make sense.
If that were the case, then when does the script actually get the array?
When the user casts a spell?
No, it does so when mysql_fetch_array() is called.

mellow

I appreciate your taking the time to reply. I am sorry for asking dumb questions. I should learn more before doing so. I will try to read the manual more completely. Sometimes when something is new it takes a while. I try to learn what happens behind the scenes.

In reply to when the result is fetched, I though that
the array was fetched because the while statement told it to

while ($rows = mysql_fetch_array($results)){

and that the value of the $rows variable(set earlier)
$rows = mysql_fetch_array($results);

merely was needed for php to know what array items to display in the printf function and did not actually function there as a command.

This probably makes no sense to you because you have a complete understanding of what is happening. I think now I am getting it--thanks.