How to avoid posting in database the same value php - php

Question

I have a problem here with break and loops things in php.I have an input type, if I give the id 2 for ex, if there is 2 in db then only "You liked this url already" should be appear.This works. If I give then id 3 it says "Data added".Good for now.But if I enter again id 3 it says:
Data added!You liked this url already
and a new value of 3 is posting in the db.How to avoid this? Here is my function:
<form method="post">
Url id: <input type="text" name="urlid" id="urlid">
<input type="submit" name="givelikes" value="Give Likes">
<br />
<br />
</form>
<?php
if(isset($_POST['givelikes'])){
$urlid = $_POST['urlid'];
$con = mysqli_connect('localhost','root','root', 'db');
$user = $_SESSION['sess_user'];
$query=mysqli_query($con,"SELECT likes FROM users WHERE user='".$user."'");
$row = mysqli_fetch_array($query);
$array = explode(" ", $row['likes']);
foreach ($array as $value) {
echo $value;
echo $urlid;
if($value == $urlid){
echo "You liked this url already";
break;
}
else{
$array = $row['likes'];
$array .= " ";
$array .= "$urlid";
$query = ("Update users set likes = '".$array."' where user = '".$user."'");
if(mysqli_query($con,$query)){
echo "Data added!";
}
else{
echo "ERROR: Could not able to execute sql: " . mysqli_error($con);
}
}
}
}
?>

Answer 1

Currently you're looping through all "likes" and comparing them. So the sequence of steps is like this:
Enter 2
No likes yet, so the data is added
Enter 2
Loop over likes, find 2, data was already added
Enter 3
Loop over likes, find 2, not match so data is added
Enter 3
Loop over likes, find 2, not match so data is added
Continue looping, find 3, data was already added
Correcting this is going to involve changing your design a bit. Right now you have one de-normalized record with a string of space-delimited "likes". Normalize your data. Have one record per "like". And instead of constantly updating a single record, insert new records.
Then when you want to see if a "like" already exists, you can use a WHERE clause. Something like this:
SELECT * FROM users WHERE user=? AND like=?
(Note: This is using query parameters as a prepared statement. This is highly recommended. Your current code is wide open to SQL injection.)
If any record is found at all, then the item was "already liked" and you can output the message. If no record was found, INSERT a new one for that "like".
No need for a loop.