MySQL更新与子查询

Question

I've got an annoying issue with an update query I'm trying to get working... The following statement SHOULD update channels.media_view_count to the result of the subquery (for all channels).

UPDATE channels c
SET c.media_view_count = (
    SELECT SUM(t.view_count)
    FROM (
      SELECT DISTINCT m.viewkey, m.view_count
      FROM media m
      INNER JOIN participants p ON m.id = p.medium_id
      WHERE p.user_id = c.id AND m.is_viewable = 1
            AND (p.pending = 0)
      ) AS t
  );

The subquery works fine independently (when specifying an actual id for c.id, like 47778 or whatever), but when I execute this statement, I get:

ERROR 1054 (42S22): Unknown column 'c.id' in 'where clause'

I thought I would be able to access the channels table (aliased as c) from within the subquery? Am I missing something or am I totally wrong here?

Any and all help is appreciated :)

Thanks,

• Jeff

Answer 1

UPDATE channels c, (
    SELECT t.user_id, SUM(t.view_count) cnt
    FROM (
      SELECT DISTINCT p.user_id, m.viewkey, m.view_count
      FROM media m
      INNER JOIN participants p ON m.id = p.medium_id
      WHERE m.is_viewable = 1
            AND (p.pending = 0)
      ) AS t GROUP BY t.user_id ) temp
SET c.media_view_count = temp.cnt
WHERE c.id =  temp.user_id

Try like this... Did not test it though :) ..
Conceptually, it should work