How Do Parameterized Queries Using Question Marks Prevent SQL Injection?

SQL Parameterized Query: The Secret of the Question Mark

When reading SQL books, you may notice that question marks (?) are often used in queries. These question marks play an important role in parameterized queries, which are widely used for dynamic SQL execution in programs.

Parameterized queries avoid using simple string queries directly, which enhances security and prevents SQL injection vulnerabilities. They act as placeholders and are dynamically assigned values ​​when the query is executed.

Consider the following example:

<code>ODBCCommand cmd = new ODBCCommand("SELECT thingA FROM tableA WHERE thingB = ?")
cmd.Parameters.Add(7)
result = cmd.Execute()</code>

Here, the question mark (?) acts as a placeholder for the dynamic value 7, which is assigned to the parameter 'thingB'. This method protects the system from malicious input that could exploit security vulnerabilities.

For example, if the user enters the following malicious input:

<code>Robert'); DROP TABLE students; --</code>

When using parameterized queries, the library will sanitize the input, and the result is:

<code>"SELECT * FROM students WHERE name = 'Robert''); DROP TABLE students; --'"</code>

Effectively prevents attackers from executing their malicious intentions.

Some database management systems (DBMS), such as MS SQL, use named parameters, improving readability and clarity. For example:

<code>cmd.Text = "SELECT thingA FROM tableA WHERE thingB = @varname"
cmd.Parameters.AddWithValue("@varname", 7)
result = cmd.Execute()</code>

By using parameterized queries with question marks, or using named parameters in some DBMS, you can protect your database from injection attacks and maintain the integrity of your data.

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