Getting multi records from check boxes - php

Question

First of all before anyone here regrets and set this duplicate I don't know will be or not but I tried to search alot but wasn't able to find my answer I created a table from which there are some checkboxes what I want to do is if someone selects 3 entries then the data will be exported for those 3 entries only this is y query what I have done so far
$id = $_POST['select'];
foreach($id as $key) {
echo $key . ", ";
}
$sql = mysqli_query($con, "SELECT * FROM $table WHERE uid IN ('$key')") or die(mysqli_error($con));
$num_rows = mysqli_num_rows($sql);
I dont know why it's giving me the last record only ? it should have given me 3 records like happens in between query it give us the entries of d between 1 and 3 but what if we select id 1 3 5 it shoulld have given these 3 right so for exporting it to excel i did this code found some help working fine but having issue with my query not successful
if($num_rows >= 1)
{
$row = mysqli_fetch_assoc($sql);
$fp = fopen($filename, "w");
$seperator = "";
$comma = "";
foreach ($row as $name => $value)
{
$seperator .= $comma . '' .str_replace('', '""', $name);
$comma = ",";
}
$seperator .= "\n";
fputs($fp, $seperator);
mysqli_data_seek($sql, 0);
while($row = mysqli_fetch_assoc($sql))
{
$seperator = "";
$comma = "";
foreach ($row as $name => $value)
{
$seperator .= $comma . '' .str_replace('', '""', $value);
$comma = ",";
}
$seperator .= "\n";
fputs($fp, $seperator);
}
fclose($fp);
echo "Your file is ready. You can download it from <a href='$filename'>here!</a>";
}
else
{
echo "There is no record in your Database";
}

Answer 1

$key is only going to be the last value in the foreach. Give the following a go:
$id = $_POST['select'];
$key = "";
foreach($id as $vals) {
$key = $key . $vals . ",";
}
$key = trim($key, ",");
$sql = mysqli_query($con, "SELECT * FROM $table WHERE uid IN ('$key')") or die(mysqli_error($con));