Why My PHP code INSERT Command is inserting duplicate data sometimes? - php

Question

Here is My Code. Its all working fine. But Some Times it inserting Duplicate Data. Why? I mean i placed the code so that same quize_no and phone combination should not submitted. But Some time its Inserting the Same quize_no and phone combination. Why is this Happening?
$sql = mysqli_query($con,"SELECT * FROM user_mm WHERE phone='$phone'");
while($row = mysqli_fetch_array($sql)) {
$name = $row['name'];
}
date_default_timezone_set("Asia/Dhaka");
$date = date('Y-m-d');
$time = date('h:i:s a', time());
$result = mysqli_query($con,"SELECT id FROM score_mm WHERE phone='$phone' AND quize_no='$quize_no' ");
$count=mysqli_num_rows($result);
if($count>0)
{
echo "1";
}
else
{
// Here I am Inserting Value in to Database
$query = mysqli_query($con,"insert into score_mm(name, phone, quize_no, score, date, time) values ('$name', '$phone','$quize_no', '$score', '$date', '$time')");
echo "Score Submitted Succesfully";
mysqli_close($con);
}

Answer 1

If there should truly never be a situation where you end up with duplicate quize_no and phone combinations in that table, then the first thing you should do is change your table structure to add a unique key to those columns.
For example:
ALTER TABLE score_mm ADD UNIQUE (quize_no, phone);
This won't fix whatever is causing multiple insert requests to be called, but it would at least protect your data integrity by not allowing any rows with duplicate value combinations.