Reused while loop only working for one selection box - php

Question

I need to generate a list of teams from the cups selection box at the top of my page, this code allows me to run a while loop to generate the correct results for the first selection box, however, when i replicate the code in the second it shows no results?
<form class="seed-form">
<select name="team" required>
<option value='Holder' disabled selected>Select Team</option> <!--Placeholder for Select-->
<?php
while ($team = mysqli_fetch_assoc($show_teams)) { ?>
<option value="<?php echo $team["team_id"]; ?>"><?php echo $team["team_name"]; ?></option>
<?php } ?> <!--FILLS SELECT BOX WITH TEAMS FROM THAT CUP-->
</select>
<select name="team" required>
<option value='Holder' disabled selected>Select Team</option> <!--Placeholder for Select-->
<?php
while ($team = mysqli_fetch_assoc($show_teams)) { ?>
<option value="<?php echo $team["team_id"]; ?>"><?php echo $team["team_name"]; ?></option>
<?php } ?> <!--FILLS SELECT BOX WITH TEAMS FROM THAT CUP-->
</select>
<input type="submit" name="submit" value="Generate" class="submit">
<?php
if (isset($_POST['submit'])) { //checking if submit button was clicked
include_once 'action/dbcon.php';
$cname = $_POST['cupname'];
if (empty($cname)) {
header("Location: tables.php?field=empty"); //return them if fields are empty
exit();
} else {
$sql = "SELECT * FROM teams WHERE cup_name='$cname'";
$show_teams = mysqli_query($conn, $sql);
$numberCheck = mysqli_num_rows($show_teams);
if ($numberCheck < 8) {
header("Location: tables.php?tables=1"); //Take to cup page if there arent enough teams in the cup
}
}
}
?>

Answer 1

The problem is that fetch_assoc() returns the next row in the resultset, unless there are no more left (in which case it returns NULL - see docs).
Your first while loop runs until there are no more results. Therefore when you start the second while loop, there are still...you guessed it: no more results. You already used them up. Therefore the first call to fetch_assoc() in the second loop returns NULL immediately, and so the loop condition is never met, and the loop never executes.
There are two different ways to solve this:
1) Reset the result pointer to the start of the resultset. Somewhere between the two loops, write
mysqli_data_seek($show_teams, 0);
See docs for more info.
2) Read all the data into a PHP array, which you can then loop through as many times as you like using foreach:
<?php
$teams = array();
while ($team = mysqli_fetch_assoc($show_teams)) {
$teams[] = $team;
}
?>
<form class="seed-form">
<select name="team" required>
<option value='Holder' disabled selected>Select Team</option> <!--Placeholder for Select-->
<?php
foreach ($teams as $team) { ?>
<option value="<?php echo $team["team_id"]; ?>"><?php echo $team["team_name"]; ?></option>
<?php } ?><!--FILLS SELECT BOX WITH TEAMS FROM THAT CUP-->
</select>
<select name="team" required>
<option value='Holder' disabled selected>Select Team</option> <!--Placeholder for Select-->
<?php
foreach ($teams as $team) { ?>
<option value="<?php echo $team["team_id"]; ?>"><?php echo $team["team_name"]; ?></option>
<?php } ?> <!--FILLS SELECT BOX WITH TEAMS FROM THAT CUP-->
</select>