PHP: mysql_fetch_array() expects parameter 1 to be resource (or mysqli_result), boolean given

If you get this message:

mysql_fetch_array() expects parameter 1 to be resource, boolean given

or

mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given

Check the $result variable or whatever name you put it before passing it to mysql_fetch_array. You'll find that it's false because the query failed. See the mysql_query documentation for possible return values and suggestions for how to deal with them.

$username = mysql_real_escape_string($_POST['username']);
$password = $_POST['password'];
$result = mysql_query("SELECT * FROM Users WHERE UserName LIKE '$username'");

if($result === FALSE) {
    die(mysql_error()); // TODO: better error handling
}

while($row = mysql_fetch_array($result))
{
    echo $row['FirstName'];
}

This example is only to illustrate what should be done (error handling), not how to do it. Production code shouldn't use or die when outputting HTML, else it will (at the very least) generate invalid HTML. Also, database error messages shouldn't be displayed to non-admin users, as it discloses too much information.

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PHP: MySQL vs Mysqli

More beyond that performance mysqli have others relevant features:

If you have a look at MySQL Improved Extension Overview, it should tell you everything you need to know about the differences between the two.

The main useful features are: - an Object-oriented interface - support for prepared statements - support for multiple statements - support for transactions - enhanced debugging capabilities - embedded server support.

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How to: Get last inserted id MySQL PHP

If you're using PDO, use PDO::lastInsertId.

If you're using Mysqli, use mysqli::$insert_id.

If you're still using Mysql:

Please, don't use mysql_* functions in new code. They are no longer maintained and are officially deprecated. See the red box? Learn about prepared statements instead, and use PDO orMySQLi - this article will help you decide which. If you choose PDO, here is a good tutorial.

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