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

Question

I saw in many tutorial that compose sql statement by using variable and Parameters.Add likt 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)

any benefit??

Solution

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.)

Comments

[Steve]

And avoid errors in string quoting just as the OP has done in its example

[saeed]

It provides an easy and fast way to parameterize queries. This yields bulletproof and simple code that accesses data.

[saeed]

It provides an easy and fast way to parameterize queries. This yields bulletproof and simple code that accesses data.

[Jon Skeet]

@Steve: I was assuming that the "..." would include the closing quote in the real query. But yes, point taken :)

[saeed]

Anything placed into a parameter will be treated as field data, not part of the SQL statement, which makes your application much more secure

[Jon Skeet]

@saeed: Isn't that covered by "avoiding SQL injection attacks"?

[saeed]

@JonSkeet of course it does! but I want to emphasis more on not a part of SQL statement