How to Use Variable Column Names with Prepared Statements in MySQL and Java?

How can I specify variable column names in a prepared statement using MySQL and Java?

String columnNames="d,e,f"; // Actually from the user...
String name = "some_table"; // From user...
String query = "SELECT a,b,c,? FROM " + name + " WHERE d=?";

In MySQL and Java, prepared statements enhance security and performance. However, they cannot be used to dynamically substitute column names directly in the SQL query after preparation. This explanation provides alternatives to achieve your goal effectively without compromising security.

// Safely construct the query manually
String columnNames="d, e, f"; // These should be validated against a whitelist before use
String name = "some_table"; // This should also be validated
String query = "SELECT a, b, c, " + columnNames + " FROM " + name + " WHERE d=?";
stmt = conn.prepareStatement(query);
stmt.setString(1, "x");

Causes

• Directly substituting column names into the prepared SQL statement leads to SQL injection vulnerabilities.
• Prepared statements only allow parameterized queries for value substitution, not for structural changes like column names.

Solutions

• Dynamically build the SQL query string using string concatenation for columns, ensuring proper input sanitization.
• Utilize a whitelist of acceptable column names to mitigate SQL injection risks when constructing the query.
• Consider using an ORM or a query builder library that allows for safer query manipulations.

Mistake: Directly passing user input as column names without validation.

Solution: Ensure all user inputs are validated against a predefined whitelist of allowed column names.

Mistake: Forgetting to sanitize user inputs, leading to SQL injection vulnerabilities.

Solution: Always implement input validation and sanitization practices.