Update query in sql commiting wrong value - php

Question

I trying to implement simple query using php in sql, but the value deducing is twice I don't know why.
What am trying to do is to get the current points of the user and reduce the points that are redeemed by the user and update the points. But what happening is suppose user have 500 points and am sending 100 points to reduce in the following php but the result shows user have 300 points remaining. Why double points are reducing in this table only.
Things i have already checked : -Calling php one time only, Checking the value of points by echo , make a separate table for checking it shows correct points.
Any help would be appreciated
<php
require "conn.php";
$conn = mysqli_connect($server_name, $mysql_username, $mysql_password, $db_name);
$number = mysqli_real_escape_string($conn, $_POST['number']);
$points = mysqli_real_escape_string($conn, $_POST['points']);
//echo $points ;
$sql1 = "UPDATE user_earning SET points = points - '$points' WHERE user_number = '$number'";
$result = $conn->query($sql1);
if ($conn->query($sql1) === TRUE) {echo "Current points Updated";
} else {echo "Error: " . $sql . "<br>" . $conn->error;
}
?>
Both $points and $number are coming from android application and am not getting any error. The response i get is current points updates. So php is running fine but the value is not coming correct in mysql

Answer 1

You're running the query twice, once each on these two lines.
$result = $conn->query($sql1);
if ($conn->query($sql1) === TRUE) {echo "Current points Updated";
The second line, maybe, should be
if ($result === TRUE) {echo "Current points Updated";

Answer 2

I think your error is here
$sql1 = "UPDATE user_earning SET points = points - '$points' WHERE user_number = '$number'";
You need the following steps
1. First retrieve the points from your table and store in a variable
$q=mysqli_query($con,"select * from user_earning");
$current_points = 0;
if($q){
while($row = mysqli_fetch_assoc($q))
$current_points = $row['points'];
}
2. Subtract the points as you want`enter code here`
$new_points = $current_points - $points.
3. Then do your update
$sql1 = "UPDATE user_earning SET points = '$new_points' WHERE user_number = '$number'";