Can PDO Prepared Statements Bind Table and Column Names, or SQL Keywords?

Can PDO Prepared Statements Bind Identifiers or Syntax Keywords?

In an attempt to construct a dynamic query with variables representing a table, a field/column, and a value to search for, one might encounter unexpected difficulties when utilizing PDO's prepared statements. Specifically, using bindParam() or bindValue() to bind these variables may result in empty result sets.

To delve into the crux of the issue, it's crucial to understand that PDO placeholders are designated to represent data literals. Therefore, attempting to use them as identifiers (like table or field names) or syntax keywords (e.g., "LIKE") can lead to erroneous behavior.

Specifically, PDO offers no inherent support for binding identifiers. This implies that developers must assume the responsibility of handling these identifiers themselves. To ensure proper execution, there are strict rules to adhere to:

Rules for Binding Identifiers:

1. Enclose identifiers within backticks.
2. Escape backticks within the identifier by doubling them.

These formatting rules prevent syntax errors and SQL injection vulnerabilities.

Rules for Binding Syntax Keywords:

1. While keyword formatting is not available, whitelisting is crucial.
2. Verify that dynamic keywords match a list of allowed values to prevent arbitrary keyword substitution.

Example:

Consider the following code snippet, which adheres to the aforementioned rules:

$allowed = array("name", "price", "qty");
$key = array_search($_GET['field'], $allowed);
$field = $allowed[$key];
$query = "SELECT $field FROM t"; // Value is safe

In summary, while PDO prepared statements excel in binding data literals, they lack support for binding identifiers or syntax keywords. By diligently following the outlined rules, developers can ensure the safe and accurate execution of dynamic queries that utilize these critical components.

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