Insert using sprintf()

Where is my script error

[henry0]

The following does not generate an error.
it is part of a longer query that I have simplified for test purposes.
if I echo $query the value is as expected and the echo stops echoing after ... VALUES ('%s')",

As I said it generates no error but does nothing! of course I can not insert

$conn = db_connect();
$query = sprintf("INSERT INTO whatever ( 'username')
VALUES ('%s')",
mysql_real_escape_string($username)
) ; echo "$query";
$result= mysql_query ($query);

PS) for test purpose I even created a table with only one field so I can't miss it :)

[henry0]

Hmmmm, lost one hour! Done.
here is my error
I had in my example ('username')
It should have been (username)

[coopster]

That didn't throw an error? I would think it might throw a ERROR 1064 [dev.mysql.com].

[henry0]

No it did not,
I would have expected one but..
and since it's on my test bed all errors are on!