用Select（PDO）和php插入

Question

Ok so I need to insert some values into a table but i need to search for one of the data in the database so i tried to do it like this

$bookid = $_GET['var'];
$username = $_GET['username'];

$quer2 = "Insert Into reserved (username,bookid) VALUES ((SELECT userid FROM users WHERE   username=:username),:var)";
$query2 = $dbc->prepare($quer2);
$query2  ->bindParam(':username',$username);
$query2  ->bindParam(':var',$bookid);
$query2 ->execute();

The problem is that I get this error

SQLSTATE[23502]: Not null violation: 7 ERROR: null value in column "username" violates not-null constraint DETAIL: Failing row contains (6, null, 2014-09-22 13:06:33.262).

I tried the query in the database and it works so I guess that there is some error in bindParam but I can't understand what it is... So if anyone could help me I would appreciate it, thank you

Answer 1

change

$query2  ->bindParam(':var',$var);

to

$query2  ->bindParam(':var',$bookid);

update your query to something like this

Insert Into reserved (username,bookid)
SELECT userid, :var FROM users WHERE username=:username

just bind the params and run the query.