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    <p>The rules of adding strings into a query are plain and simple:</p> <ol> <li>The string should be enclosed in quotes.</li> <li>Therefore, these quotes should be escaped in the data, as well as some other characters, using <code>mysql_real_escape_string()</code></li> </ol> <p>So, your code becomes</p> <pre><code>$type = 'testing'; $type = mysql_real_escape_string($type); $reporter = "John O'Hara"; $reporter = mysql_real_escape_string($reporter); $query = "INSERT INTO contents (type, reporter, description) VALUES('$type', '$reporter', 'whatever')"; mysql_query($query) or trigger_error(mysql_error()." in ".$query); // note that when running mysql_query you have to always check for errors </code></pre> <p>But if you're going to add the variable in another part of a query, the rules change. </p> <ul> <li>To add a number, you have to cast it to its type explicitly. </li> </ul> <p>For example:</p> <pre><code>$limit = intval($_GET['limit']); //casting to int type! $query = "SELECT * FROM table LIMIT $limit"; </code></pre> <ul> <li>To add an identifier, it's better to choose it from some sort of white list, consists of hardcoded values</li> </ul> <p>For example:</p> <pre><code>if ($_GET['sortorder'] == 'name') { $sortorder = 'name'; } else { $sortorder = 'id'; } $query = "SELECT * FROM table ORDER BY $sortorder"; </code></pre> <p><strong>To make it all simplified</strong> yet with guaranteed safety, one have to use some sort of <strong>placeholder system</strong> where the variable goes into a query not directly but via some proxy, called a placeholder.</p> <p>So, your query call becomes something like this:</p> <pre><code>$type = 'testing'; $reporter = "John O'Hara"; pquery("INSERT INTO contents (type, reporter, description) VALUES(?s, ?s, ?s)", $type, $reporter,'whatever'); </code></pre> <p>And there will be absolutely no need to worry about all these matters.</p> <p>For the limited set of placeholders you can use <a href="https://stackoverflow.com/tags/pdo/info">PDO</a>. Though for real life usage you will need extended set which is offered by but a few libraries, one of which is <a href="https://github.com/colshrapnel/safemysql" rel="noreferrer">SafeMysql</a>.</p>
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    1. POHow to include a PHP variable inside a MySQL insert statement
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    1. COWhat is `pquery()`?
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    2. CO@Starx that's just a fictional function to show the idea. I know no library providing such a feature though.
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    3. CO@YourCommonSense: Erm, any PDO.
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