Discuss what is the best way to prevent SQL injection in PHP

Discuss what is the best way to prevent SQL injection in PHP_PHP Tutorial

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Release： 2016-07-21 15:06:50

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If the user enters a query that is inserted directly into a SQL statement, the application will be vulnerable to SQL injection, such as the following example:

Copy codeThe code is as follows:

$unsafe_variable = $_POST['user_input'];
mysql_query("INSERT INTO table (column) VALUES ('" . $unsafe_variable . "')") ;

This is because the user can enter something like VALUE"); DROP TABLE table; - , making the query become:

Copy code The code is as follows:

INSERT INTO table (column) VALUES('VALUE'); DROP TABLE table;'

What should we do How to prevent this? Please see below
Use prepared statements and parameterized queries. SQL statements with any parameters will be sent to the database server and parsed! It is impossible to maliciously inject sql!
There are basically two options to achieve this goal:
1. Use PDO (PHP Data Objects):

Copy code The code is as follows:

$stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name ');
$stmt->execute(array(':name' => $name));
foreach ($stmt as $row) {
 // do something with $row
}

2. Use mysqli:

Copy code Code As follows:

$stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
$stmt->bind_param('s', $name) ;
$stmt->execute();
$result = $stmt->get_result();
while ($row = $result->fetch_assoc()) {
 / / do something with $row
}

PDO (PHP Data Object)
Note the real preparation when using PDO to access the MySQL database The meaning statement is not used by default! To resolve this issue, you must disable emulation of prepared statements.
An example of using PDO to create a connection is as follows:

Copy the code The code is as follows:

$ dbConnection = new PDO('mysql:dbname=dbtest;host=127.0.0.1;charset=utf8', 'user', 'pass');
$dbConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false); 
$dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

The error mode ERRMODE is not strictly necessary in the above example, but it is recommended to add it. This method does not stop the script when a fatal error occurs. And give the developer a chance to catch any errors (when PDOException is thrown). The
setAttribute() line is mandatory. It tells PDO to disable simulated prepared statements and use real prepared statements. This ensures that statements and values are not parsed by PHP before being sent to the MySQL database server (an attacker has no chance of injecting malicious SQL).
Of course you can set the character set parameter in the constructor options, paying special attention to the 'old' one PHP version (5.3.6) will ignore the character set parameter in the DSN.

Explanation
What happens when the SQL prepared statement you pass is parsed and compiled by the database server? Tell the database engine what you want to filter by specifying characters (like a? or like: name in the above example). Then call execute to execute the combined prepared statement and the parameter value you specified.

here Most importantly, the parameter value is combined with a precompiled statement, not with a SQL string. SQL injection works by deceptively creating a SQL script that includes a malicious string and sends it to the database. Therefore, by sending By actually separating the sql parameters, you will reduce the risk. When using prepared statements, any parameters you send, will only be treated as strings (although the database engine may do some parameter optimization, which of course may end up as numbers ). In the above example, if the variable $name contains 'sarah';DELETE * FROM employees, the result will only be a search string "'sarah';DELETE * FROM employees", and you will not get an empty table.

Another benefit of using prepared statements is that if you execute the same statement multiple times in the same session, this will only be parsed and compiled once, giving you some speed gain.
Oh, since you asked how to do the insert, here is an example (using PDO):

Copy the code The code is as follows:

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