To Update a Database in PHP MySqli you will have to make sure that the following steps have been taken.

1. You Created A Database
2. You Granted Privileges to the database
3. Created a config.php file to access the database
4. Make sure you Connect to a Database before using this code.

The purpose of updating a database is that you will make the information within the database different. You will be updating values within a table row. This is different than inserting into a database. You will actually change whatever value is in there.

mysqli_query($con,"UPDATE table SET row1='$var'
WHERE username='$var' ");

OR like this.

$sql = "UPDATE MyGuests SET lastname='Doe' WHERE id=2";

if ($conn->query($sql) === TRUE) {
  echo "Record updated successfully";
} else {
  echo "Error updating record: " . $conn->error;
}

Update with prepared statements.

$stmt = $conn->prepare("UPDATE equipment SET `type` = ?, `name` = ?, `year` = ?, `value` = ? WHERE `id` = ?");
$stmt->bind_param("sisdi", $type, $name, $year, $value, $eqid);
$stmt->execute();
$stmt->close();

Update a Database in PHP MySqli

Remember that you will have to include the config file for this to work. You can put include('config.php'); at the top of the file. Right below that you will have to make sure that you are using the connection code to the database code.