Logic operation failure in php - php

Question

I want to do some logic operation before updating the data in MySQL. However, I think there are some problems in my logic operation. I do not know which line causes the problem. Can anyone help?
<?php
session_start();
if ($_POST['meetingid'] > $_SESSION["id"]){
echo "ERROR: Wrong Meeting_ID. Update failed.<br>";
}
else if(empty($_POST['date'])) {
echo "ERROR: No empty data field is allowed. Update failed. (Date field)<br>";
}
else if(empty($POST['committee'])) {
echo "ERROR: No empty data field is allowed. Update failed. (Committee field)<br>";
}
else if(empty($_POST['session'])) {
echo "ERROR: No empty data field is allowed. Update failed. (Session field)<br>";
}
else{
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = 'admin123';
$conn = mysql_connect($dbhost, $dbuser, $dbpass);
if(! $conn ) {
die('Could not connect: ' . mysql_error());
}
$meetingid = $_POST['meetingid'];
$date = $_POST['date'];
$committee = $_POST['committee'];
$session = $_POST['session'];
$sql = "UPDATE `meeting` SET `Date`='$date' ,`Committee`='$committee' ,`Session`='$session' WHERE `Meeting_ID`='$meetingid'" ;
mysql_select_db('imo resolution v.2');
$retval = mysql_query( $sql, $conn );
if(! $retval ) {
die('Could not update data: ' . mysql_error());
}
else{
echo "Updated data successfully<br>";
}
mysql_close($conn);
}
?>

Answer 1

Here is the code refactored (untested)
Some notes about what has changed:
Changed the initial condition because what would happen if $_POST['meetingid'] was less than $_SESSION['id'] but not equivalent.
Combined the empty() statements together. Your code before would not display correctly if your form had more than 1 empty field.
mysql_ functions are deprecated. Don't use them! Use mysqli_ instead.
Added some basic santisation through mysqli_real_escape_string() function
Removed mysql_select_db() as you can set the database through mysqli_connect()
Updated the code to check whether the INSERT statement was successful
<?php
session_start();
if ($_POST['meetingid'] !== $_SESSION['id']) {
echo 'ERROR: Wrong Meeting ID';
} else if (empty($_POST['date']) || empty($_POST['committee']) || empty($_POST['session'])) {
echo 'Error inserting due to empty field';
print_r($_POST);
} else {
$dbhost = 'localhost';
$dbuser = 'root';
$dbpass = '';
$dbdb = 'imo_reslution_v.2';
$conn = mysqli_connect($dbhost, $dbuser, $dbpass, $dbdb);
if(! $conn ) {
die('Could not connect: ' . mysqli_error());
}
$meetingid = mysqli_real_escape_string($conn, $_POST['meetingid']);
$date = mysqli_real_escape_string($conn, $_POST['date']);
$committee = mysqli_real_escape_string($conn, $_POST['committee']);
$session = mysqli_real_escape_string($conn, $_POST['session']);
$sql = "UPDATE `meeting` SET `Date`='$date' ,`Committee`='$committee' ,`Session`='$session' WHERE `Meeting_ID`='$meetingid'" ;
$retval = mysqli_query( $sql, $conn );
if( mysqli_infected_rows() == 0 ) {
die('Could not update data: ' . mysqli_error());
}else {
echo "Updated data successfully<br>";
}
mysqli_close($conn);
}
?>

Answer 2

Warning mysql_query, mysql_fetch_array,mysql_connect etc.. extensions were deprecated in PHP 5.5.0, and it was removed in PHP 7.0.0.
Instead, the MySQLi or PDO_MySQL extension should be used.
As per mulqin suggestion (untested)
try to use prepared statement to avoid sql injections
<?php
session_start();
if ($_POST['meetingid'] !== $_SESSION['id']) {
echo 'ERROR: Wrong Meeting ID';
} else if (empty($_POST['date']) || empty($_POST['committee']) || empty($_POST['session'])) {
echo 'Error inserting due to empty field';
print_r($_POST);
} else {
//db connection
global $conn;
$servername = "localhost"; //host name
$username = "root"; //username
$password = "admin123"; //password
//mysqli prepared statement
$conn = mysqli_connect($servername, $username, $password) or die("Connection failed: " . mysqli_connect_error());
mysqli_select_db($conn,`imo_resolution_v.2`) or die("Opps some thing went wrong");
$stmt = $conn->prepare("UPDATE `meeting` SET `Date`=? ,`Committee`=? ,`Session`=? WHERE `Meeting_ID`=? ");
$stmt->bind_param('ssii',$date,$committee,$session,$meetingid);
The argument may be one of four types:
i - integer
d - double
s - string
b - BLOB
//change it by respectively
$stmt->execute();
$row_count= $stmt->affected_rows;
$stmt->close();
$conn->close();
if($row_count>0)
{
echo "Updated data successfully<br>";
}
else
{
echo "Not Updated";
}
}
?>