PHP While loop only echoes once - php

Question

this is the PHP code i have:
while($row1 = mysql_fetch_object($query1)) {
echo "*".$row1->id."*";
while ($row2 = mysql_fetch_object($query2)) {
echo "%".$row2->id."%";
}
}
I want it to output for example: *1*%1%%2%%3%%4%*2*%1%%2%%3%%4%*3*%1%%2%%3%%4%
But what this loop outputs is: *1*%1%%2%%3%%4%*2**3*
(It only outputs the $row2 values in the first loop of $row1.
How can I fix this? Thanks.

Answer 1

A few things to note about mysql_fetch_object(). From the PHP document:
Warning: This extension is deprecated as of PHP 5.5.0
Please note above.
returns an object with properties that correspond to the fetched row and moves the internal data pointer ahead.
Please note what I bolded.
The $result object (in your code this would be $query2) is an iterative object that has a pointer pointing to the current item.
Current Item
|
v
[1][2][3][4]
When your first loop hits your second loop, it iterates over the whole thing, such that at the end, the object now looks something like this:
Current Item
|
v
[1][2][3][4]
For each iteration of the first loop, after the first time, the mysql_fetch_object() function basically goes like this:
mysql_fetch_object() ~
1. Get the next time
2. Uh, there are no more objects because we're at item [4]. Return done.
So, how do you get it to work? You could simply save the results into an array and then iterate over that array or you can reset the pointer with mysql_data_seek() (which is also deprecated as of 5.5).
To reset the data pointer, it would be something like this:
while($row1 = mysql_fetch_object($query1)) {
echo "*".$row1->id."*";
while ($row2 = mysql_fetch_object($query2)) {
echo "%".$row2->id."%";
}
// put the result pointer back to the front
mysql_data_seek($query2, 0)
}
Note1, This SO question/answer helped me find the function to use to reset the pointer.
Note, the downside is that you're calling a function that's creating an object, which creates processing overhead every time it runs.
The other option would be save the results into an array and just loop through the array every time:
$secondary_result = array();
while ($row2 = mysql_fetch_object($query2)) {
$secondary_result[] = $row2;
}
while($row1 = mysql_fetch_object($query1)) {
echo "*".$row1->id."*";
foreach($secondary_result as $row2) {
echo "%".$row2->id."%";
}
}
Note, this method will be creating extra memory usage of storing the objects in an array, but it would save on CPU processing as you're not re-creating the objects over and over again, as well as calling a function.
If you just print output, you can consider just saving the result first. No matter now many times you loop over $secondary_result, the final result will always be the same (as per your code, the first loop shows no signs of being directly influencing the second result).
In that case, this makes much more sense
$buffer = '';
while ($row2 = mysql_fetch_object($query2)) {
$buffer .= "%".$row2->id."%";
}
while($row1 = mysql_fetch_object($query1)) {
echo "*".$row1->id."*";
echo $buffer;
}
but I really don't know why you'd do that. If you're doing a nested loop, usually it's because the result of the first loop is affecting the second loop.
But I hope that helps!
Cheers!
EDIT
Per #Blazemonger's comment about looking ahead, the PDO equivalent would be: MySqli:Fetch-Object
When you have a result object from using the PDO function, you would loop like this:
while($row1 = $query1->fetch_object()) {
echo "*".$row1->id."*";
while ($row2 = $query1->fetch_object()) {
echo "%".$row2->id."%";
}
// put the result pointer back to the front
$query2->data_seek(0);
}
The above example shows both the fetch Object and pointer reset versions of MySqli.

Answer 2

The problem is that once you iterate fully through $query2, that's the end of your results. The next time through your $row1 loop, you're still at the end of $query2 and have no results left. Try using mysql_data_seek to go back to the start of your results:
while($row1 = mysql_fetch_object($query1)) {
echo "*".$row1->id."*";
mysql_data_seek($query2, 0);
while ($row2 = mysql_fetch_object($query2)) {
echo "%".$row2->id."%";
}
}

Answer 3

if you really need to repeat your second query data many times, get it into array first, and loop over this array as many times as you need.

Answer 4

First of all: The mysql_* functions are deprecated and will be removed in PHP 5.5. Consider using mysqli or PDO instead.
That being said; back to your question:
Each result set contains an internal pointer to one of the records in the result set. Initially, this pointer points to the first record, and is advanced with each call to mysql_fetch_object.
After your first inner loop, the internal pointer of the $query2 result set will already be at the end of the list, so subsequent calls to mysql_fetch_object will only return FALSE.
If your inner query depends on values from $row1, you will need to re-execute the second query within your outer loop. Otherwise, you can reset the result pointer with mysql_data_seek.

Answer 5

Perhaps you're not getting anything when you call $row2 = mysql_fetch_object($query2) which would give you the output you're getting.

Answer 6

After the first loop there are no more results for query2 to return. So the while is false in each additional loop. You would want to reset the query with mysqli_data_seek or storing all the data in a separate array and looping through that instead.
Please also note:
Per the documentation http://us2.php.net/manual/en/function.mysql-fetch-object.php
The mysql extension is deprecated as of PHP 5.5.0, and will be removed
in the future. Instead, the MySQLi or PDO_MySQL extension should be
used