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I have searched the net and so far what I have seen is that you can use mysql_ and mysqli_ together meaning:

$con=mysqli_connect("localhost", "root" ,"" ,"mysql");

if( mysqli_connect_errno( $con ) ) {
    echo "failed to connect";
    echo "connected";
echo "Done";


$con=mysql_connect("localhost", "root" ,"" ,"mysql");
if( mysqli_connect_errno( $con ) ) {
    echo "failed to connect";
    echo "connected";
echo "Done";

Are valid but when I use this code what I get is:

Warning: mysql_close() expects parameter 1 to be resource, object given in D:************.php on line 9

For the first and the same except with mysqli_close(). For the second one.

What is the problem? Can't I use mysql_ and mysqli together? Or is it normal? Is the way I can check if the connections are valid at all? (the if(mysq...))



No, you can't use mysql and mysqli together. They are separate APIs and the resources they create are incompatible with one another.

There is a mysqli_close, though.

Tuesday, November 22, 2022

Use prepared statements and parameterized queries. These are SQL statements that are sent to and parsed by the database server separately from any parameters. This way it is impossible for an attacker to inject malicious SQL.

You basically have two options to achieve this:

  1. Using PDO (for any supported database driver):

    $stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
    $stmt->execute([ 'name' => $name ]);
    foreach ($stmt as $row) {
        // Do something with $row
  2. Using MySQLi (for MySQL):

    $stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
    $stmt->bind_param('s', $name); // 's' specifies the variable type => 'string'
    $result = $stmt->get_result();
    while ($row = $result->fetch_assoc()) {
        // Do something with $row

If you're connecting to a database other than MySQL, there is a driver-specific second option that you can refer to (for example, pg_prepare() and pg_execute() for PostgreSQL). PDO is the universal option.

Correctly setting up the connection

Note that when using PDO to access a MySQL database real prepared statements are not used by default. To fix this you have to disable the emulation of prepared statements. An example of creating a connection using PDO is:

$dbConnection = new PDO('mysql:dbname=dbtest;host=;charset=utf8', 'user', 'password');

$dbConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
$dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

In the above example the error mode isn't strictly necessary, but it is advised to add it. This way the script will not stop with a Fatal Error when something goes wrong. And it gives the developer the chance to catch any error(s) which are thrown as PDOExceptions.

What is mandatory, however, is the first setAttribute() line, which tells PDO to disable emulated prepared statements and use real prepared statements. This makes sure the statement and the values aren't parsed by PHP before sending it to the MySQL server (giving a possible attacker no chance to inject malicious SQL).

Although you can set the charset in the options of the constructor, it's important to note that 'older' versions of PHP (before 5.3.6) silently ignored the charset parameter in the DSN.


The SQL statement you pass to prepare is parsed and compiled by the database server. By specifying parameters (either a ? or a named parameter like :name in the example above) you tell the database engine where you want to filter on. Then when you call execute, the prepared statement is combined with the parameter values you specify.

The important thing here is that the parameter values are combined with the compiled statement, not an SQL string. SQL injection works by tricking the script into including malicious strings when it creates SQL to send to the database. So by sending the actual SQL separately from the parameters, you limit the risk of ending up with something you didn't intend.

Any parameters you send when using a prepared statement will just be treated as strings (although the database engine may do some optimization so parameters may end up as numbers too, of course). In the example above, if the $name variable contains 'Sarah'; DELETE FROM employees the result would simply be a search for the string "'Sarah'; DELETE FROM employees", and you will not end up with an empty table.

Another benefit of using prepared statements is that if you execute the same statement many times in the same session it will only be parsed and compiled once, giving you some speed gains.

Oh, and since you asked about how to do it for an insert, here's an example (using PDO):

$preparedStatement = $db->prepare('INSERT INTO table (column) VALUES (:column)');

$preparedStatement->execute([ 'column' => $unsafeValue ]);

Can prepared statements be used for dynamic queries?

While you can still use prepared statements for the query parameters, the structure of the dynamic query itself cannot be parametrized and certain query features cannot be parametrized.

For these specific scenarios, the best thing to do is use a whitelist filter that restricts the possible values.

// Value whitelist
// $dir can only be 'DESC', otherwise it will be 'ASC'
if (empty($dir) || $dir !== 'DESC') {
   $dir = 'ASC';
Wednesday, August 3, 2022

The following works for me:


$pdo = new PDO("mysql:host=localhost;dbname=test", "root", "pass");
$pdo->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

$stmt = $pdo->prepare("INSERT INTO `null_test` (`can_be_null`) VALUES (:null)");
$stmt->bindValue(":null", null, PDO::PARAM_NULL);


Pass in PHP's null, with type of PDO::PARAM_NULL. Also, make sure your prepare emulation is set to false. That might help.

Sunday, August 7, 2022

First of all, you should make it a bit more safe:

mysql_query(sprintf("UPDATE offtopic SET next = '%s' WHERE id = '%s'",

Now, is your id actually string, and not numeric? If its numeric, you should rather have:

mysql_query(sprintf("UPDATE offtopic SET next = '%s' WHERE id = %d",
            mysql_real_escape_string($insert), $id);
Friday, November 18, 2022

Your PDO is configured to emulate prepared queries, whereas mysqli is using true prepared queries.

The prepared query binds the string ''1'' as an integer parameter value. PHP coerces it to an integer using something like intval(). Any string with non-numeric leading characters is interpreted as 0 by PHP, so the parameter value sent after prepare is the value 0.

The fake prepared query uses string interpolation (instead of binding) to add the string ''1'' into the SQL query before MySQL parses it. But the result is similar, because SQL also treats a string with non-numeric leading characters in an integer context as the value 0.

The only difference is what ends up in the general query log when the parameter is bound before prepare versus after prepare.

You can also make PDO use real prepared queries, so it should act just like mysqli in this case:

$dbh->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);

PS: This may demonstrate a good reason why it's customary to start id values at 1 instead of 0.

Monday, October 10, 2022
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