How to prevent SQL injection in PHP (2)

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:

<code><span>$unsafe_variable</span> = <span>$_POST</span>[<span>'user_input'</span>];
mysql_query(<span>"INSERT INTO table (column) VALUES ('"</span> . <span>$unsafe_variable</span> . <span>"')"</span>);</code>

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

<code><span><span>INSERT</span><span>INTO</span><span>table</span> (<span>column</span>) <span>VALUES</span>(<span>'VALUE'</span>);</span><span><span>DROP</span><span>TABLE</span><span>table</span>;</span>'</code>

How should we prevent this situation? Let’s take a look at Theo’s answer
Use prepared statements and parameterized queries. SQL statements with any parameters will be sent to the database server and parsed! It is impossible for an attacker to maliciously inject SQL!
There are basically two options to achieve this goal:

1. Use PDO (PHP Data Objects)

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

2. Use mysqli

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

PDO (PHP Data Objects)
Note that when using PDO to access the MySQL database, the actual prepared statements are 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:

<code><span>$dbConnection</span><span>=</span><span>new</span> PDO(<span>'mysql:dbname=dbtest;host=127.0.0.1;charset=utf8'</span>, <span>'user'</span>, <span>'pass'</span>);
<span>$dbConnection</span><span>-></span>setAttribute(PDO<span>::ATTR_EMULATE_PREPARES</span>, <span>false</span>);
<span>$dbConnection</span><span>-></span>setAttribute(PDO<span>::ATTR_ERRMODE</span>, PDO<span>::ERRMODE_<strong>Exception</strong></span>);</code>

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 PDO Exception exception is thrown).
The setAttribute() line is mandatory, it tells PDO to disable emulated 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 (there is no chance for an attacker to inject malicious SQL).
Of course you can set the character set parameter in the constructor options, especially note that 'old' PHP versions (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.
The most important thing here is that 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 By sending actual separate 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 may of course end up being Number). 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", 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, and since you asked how to do the insert, here's an example (using PDO):

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

http://www.jb51.net/article/36042.htm

The above introduces the method (2) of preventing SQL injection in PHP, including the relevant content. I hope it will be helpful to friends who are interested in PHP tutorials.