如何计算此SQL查询？

Question

I'm trying to figure out how to count this query with a left join:

$friends_q = mysql_query("SELECT ava_users.*
FROM ava_friends
LEFT JOIN ava_users 
ON ava_friends.user2 = ava_users.id
WHERE ava_friends.user1 = $user[id]");

This was my approach:

$total_results = mysql_result(mysql_query("
SELECT
    ava_users.*, COUNT(*) as Num
FROM ava_friends
    LEFT JOIN ava_users ON ava_friends.user2 = ava_users.id
WHERE ava_friends.user1 = $user[id]"), 0);

This doesn't work. All I get is a "PHP Warning: mysql_result() expects parameter 1 to be resource, boolean given[...]" error.

Answer 1

If you want more than ava_users.id (from the first table) - pull the fields by their names (don't use ava_users.* ) and change group by respectively.

SELECT ava_users.id, count(ava_friends.user2) as "Counter"
FROM ava_friends
LEFT JOIN ava_users 
ON ava_friends.user2 = ava_users.id
WHERE ava_friends.user1 = $user[id]
group by ava_users.id

Comment :
Do not use mysql_* functions - its deprecated (see the red box ) and vulnerable to sql-injection. Use PDO or MySQLi instead.