Using Variables in MySQL Update (Php/Mysql)

How to update database using PHP variables?

First off, never use the deprecated mysql_* API.

Switch to either PDO or mysqli, both have prepared statements, which would make your code a tad bit more safe when it comes to SQL-Injections (which your code is very open for).

When a query fails, the mysql_error() global function will return the latest mysql error.

The easiest way to get information about a failing query is by adding or die(mysql_error()); after the query execution.

Example with your code:

$result = mysql_query($query) or die(mysql_error());

This will report your error and stop execute the script.

Your sql code is slightly wrong (as RST mentions), you are missing a comma between the values you are trying to set.

Using mysqli and prepared statements, your code could look something like:

// Using the mysqli object oriented style.
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$mysqli = new mysqli('localhost', 'username', 'password', 'database');

// Prepare the statement.
$statement = $mysqli->prepare('UPDATE billdata SET Total=?, Due=? WHERE InvoiceNo=?');
// The question marks is placeholders for the input that will be added in a while.

// Bind your parameters (ssi tells mysqli what type of params it is, s = string, i = int).
$statement->bind_param('ssi', $total, $due, $invoceno);
// Execute the statement.
$statement->execute();

// Cleanup.
$statement->close();
$mysqli->close();

PHP MYSQL Update Query with @variable not working

You can't put multiple queries in a single call to mysql_query(). Split it into two calls:

$query = 'SET @order := 0'; 
mysql_query($query) OR die(mysql_error());
$query = 'UPDATE `task` SET `order` = @order := @order + 10 WHERE project = "'.$project.'";';
mysql_query($query) OR die(mysql_error());

Variables like @order persist between calls, since they're associated with the connection, not the call.

PHP - using update with variables

The value for $username should be wrap with single quotes.

mysql_query(" UPDATE table_name 
                 SET int_field = '$int_value' 
               WHERE username = '$username'");

SideNote: your code is vulnerable with SQL Injection. Please read the article below to know how to secure your code,

Best way to prevent SQL injection in PHP?

Is there a way to use a variable in a MySQL update query

Most Importantly: Your query is open to SQL Injection related attacks. Please learn how to use Prepared Statements

Also, it seems that the value of your $lhs variable is a Reserved keyword in MySQL. It is incidentally your column name as well. So, you need to use backticks (`), asking MySQL to consider it as a column/table/database name or some aliased expression.

Now, just do the following, to use $lhs as a column in the Update query:

$update = "UPDATE table1 `" .
          $lhs . "` = '" . $rhs . "' 
          WHERE id = '".$_SESSION['id']."' ";

mysqli_query($conn, $update);

passing php variable in mysql update

You have errors in your query, use this

UPDATE stud SET name='$name', lect ='$lectr', atnds ='$atndsr'  
WHERE id = '$id' LIMIT 1

and you just wrote the query, not performing it, for that you have to use mysqli_query() or mysql_query() function....please let me know if you have any more doubts. and even in your $_POST global variable you have used

$lectr = $_POST[$lect][$i];   $atndsr = $_POST[$atnds][$i];

I know that it is not correct way. So, please before querying print out $_POST global variable and then use those keys in above. It could be like this

$lectr = $_POST['lect'][$i];
$atndsr = $_POST['atnds'][$i];