Can I Bind Identifiers and Keywords in PHP PDO Prepared Statements?

Binding Identifiers and Syntax Keywords in PHP PDO Prepared Statements

Dynamic queries allow for flexible database operations by utilizing variables to define table names, column names, and search values. However, binding identifiers (table or field names) or syntax keywords using PDO prepared statements can lead to unexpected results.

Issue:

When using bindParam() or bindValue() to bind variables representing identifiers or syntax keywords, an empty array is returned instead of the expected database results.

Explanation:

PDO prepared statements can bind data literals only. Therefore, attempting to bind identifiers or keywords will not result in the desired outcome.

Solution:

To create secure and reliable dynamic queries, it is crucial to:

• Format identifiers properly: Enclose identifiers in backticks (') and escape backticks inside by doubling them (```).
• Use whitelisting: Validate dynamic identifiers against a hardcoded list of allowed values to prevent potential injections.
• Apply the same rules to syntax keywords: Whitelist and validate all syntax keywords used in dynamic queries.

Code Example:

To format and validate an identifier:

$field = "`" . str_replace("`", "``", $field) . "`";

To whitelist and validate a keyword:

$dir = $_GET['dir'] == 'DESC' ? 'DESC' : 'ASC'; 

Then, include the sanitized variables in the prepared statement:

$stmt = $db->prepare('
    SELECT 
        * 
    FROM 
        ?
    WHERE 
        ? LIKE ?
');
$stmt->bindParam(1, $searchTable);
$stmt->bindParam(2, $searchBy);
$stmt->bindValue(3, '%' . $searchTerm . '%');

By adhering to these rules, you can ensure the validity and security of your dynamic database queries.

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