php&mysql:下面哪个查询更快?为什么?

1. 以下3个查询中哪一个更快?为什么?
2. 我在我的应用程序中使用了很多其他连接的查询。那么,我有没有什么方法可以测试他们的速度呢?如果是,你能告诉我是什么吗?

查询1:

$q = "SELECT COUNT(books.id) FROM books 
INNER JOIN books_type ON books.id = books_type.id
WHERE books_type.book_type = 'Comedy'";

查询2:

$q = "SELECT COUNT(*) FROM books 
INNER JOIN books_type ON books.id = books_type.id
WHERE books_type.book_type = 'Comedy'";

查询3:

$q = "SELECT books.id FROM books 
INNER JOIN books_type ON books.id = books_type.id
WHERE books_type.book_type = 'Comedy'";

$books_count = mysql_num_rows($q);

谢谢您。