How to properly update a SQL table row using PHP - php

Question

Current update: I've cleaned up the code, and there are still some issues.
NOTE this code runs every 3 seconds. The outermost 'else' statement seems to run, setting the time to 0 in the database table, but then there is no activity.
After the initial time of running, the outermost 'else' statement should never run, and the time value stored under the user's alias should keep updating with the latest time stamp, but it just sits at '0'.
This is the JS that runs the php file:
//CHECK FOR NEW CHAT MESSAGES
setInterval(function()
{
$.post("chat_update.php", function(data) { $("#rect_comments_text").append(data);} );
}, 3000);
Code:
<?php
session_start();
$alias = $_SESSION['username'];
$host = 'localhost';
$user = '*';
$pass = '*';
$database = 'vethergen_db_accounts';
$table = 'table_messages';
$time_table = 'table_chat_sync';
$connection = mysqli_connect($host, $user, $pass) or die ("Unable to connect!");
mysqli_select_db($connection,$database) or die ("Unable to select database!");
$timestamp = time();
$last_time_query = "SELECT alias FROM $time_table";
$last_time_result = mysqli_query($connection,$last_time_query);
$last_time_rows = mysqli_fetch_array($last_time_result);
if ($last_time_rows['alias'] === $alias)
{
$last_time = $last_time_rows['time'];
$query = "SELECT * FROM $table WHERE time > $last_time ORDER BY text_id ASC"; //SELECT NEW MESSAGES
$result = mysqli_query($connection,$query);
//APPEND NEW MESSAGES
while($row = mysqli_fetch_array($result))
{
if ($row['alias'] === "Vether")
{
echo '<p id = "chat_text">'.'<b>'.$row['alias'].'</b>'.': '.$row['text']."</p>";
echo '<p id = "time_stamp">'.$row['time'].'</p>';
echo '<p id = "chat_number">'.$row['text_id'].'</p>';
}
else
{
echo '<p id = "chat_text">'.'<b class = "bold_green">'.$row['alias'].'</b>'.': '.$row['text']."</p>";
echo '<p id = "time_stamp">'.$row['time'].'</p>';
echo '<p id = "chat_number">'.$row['text_id'].'</p>';
}
echo '<hr class = "chat_line"></hr>';
}
//UPDATE LAST SYNC TIME
$update_query = "UPDATE $time_table SET time = '$timestamp' WHERE alias = '$alias'";
mysqli_query($connection,$update_query);
}
else
{
echo '<p> HERE </p>';
$update_query = "INSERT INTO $time_table (alias, time) VALUES('$alias','0')";
mysqli_query($connection,$update_query);
}
?>

Answer 1

You try this
$sql_update = "UPDATE time_table SET time= '$timestamp' WHERE alias = '$alias'";
if ($con->query($sql_update ) === TRUE) {
}
else{
echo "Error: " . $sql_update . "<br>" . $con->error;
}

Answer 2

You need to only check mysqli_num_rows to whether to insert or update data. You have to add ' around $alias in select query also. change your code as below:
//EITHER UPDATE THE EXISTING VALUE OR CREATE ONE FOR FIRST TIME VISITORS...
$last_time_query = "SELECT * FROM $time_table WHERE alias = '$alias'"; //change here add '
$last_time_result = mysqli_query($connection,$last_time_query);
if (mysqli_num_rows($last_time_result) == 0) //Only check number of rows
{
$update_query = "INSERT INTO $time_table (alias, time) VALUES('$alias','$timestamp')";
mysqli_query($connection,$update_query);
}
else
{
$update_query = "UPDATE $time_table SET time = '$timestamp' WHERE alias = '$alias'";
mysqli_query($connection,$update_query);
}