Why we do SQLiteCommand, Parameters.add while we can use string.Format to compose sql statement?

Question

Many tutorials I've seen compose SQL statements by using variables and Parameters.Add, like this:

public void updateStudent(String @studentID, String @firstName, String @lastName)
{
    SQLiteCommand command = conn.CreateCommand();
    command.CommandText = "UPDATE Students SET firstName = @firstName, lastName = @lastName WHERE studentID = @studentID";
    command.Parameters.Add(new SQLiteParameter("@studentID", @studentID));
    command.Parameters.Add(new SQLiteParameter("@firstName", @firstName));
    command.Parameters.Add(new SQLiteParameter("@lastName" , @lastName));
    command.ExecuteNonQuery();
}

Why don't we use

string.Format("Update Students SET firstName = '{0}', lastName = '{1}...", @firstName, @lastname)

instead?

Answer 1

Four reasons:

• Avoiding SQL injection attacks
• Avoiding problems with strings containing genuine apostrophes with no intention of causing a SQL injection attack (e.g. a last name of "O'Reilly"
• Avoiding string unnecessary conversions, which can cause failures for cultural reasons (e.g. the difference between "1.23" and "1,23" depending on your culture
• Keeping the code (SQL) and the data (parameters) separate for cleaner readability

Also note:

• This isn't SQLite specific. It's best practice for all databases.

• You don't need to use @ as a prefix to your variables unless they're keywords. So it would be more idiomatic to write:

  command.Parameters.Add(new SQLiteParameter("@lastName", lastName));
  

  (Ditto for the method parameter declarations to start with... but not the parameters inside the SQL statement.)