MySQL选择不同的计数

Question

+----------+----------+
| user_id  | video_id |
+----------+----------+
|        1 |    1     |
|        1 |    1     |
|        1 |    2     |
|        2 |    1     |
|        2 |    2     |
+----------+----------+

I have a table setup similar to the one above. I would like to return a total count from my query.

For each user_id they need to have a DISTINCT video_id . So above, user_id = 1 would have 2 unique video_id's and user_id = 2 would have 2 unique video_id's. This would make the total 4. I'm not sure the best way to organize my query to achieve the desired result.

Basically for each user_id, I need something like, COUNT(DISTINCT video_id)

I would like the final result just to return total count of everything.

Answer 1

If you want to get the total count for each user, then you will use:

select user_id, count(distinct video_id)
from data
group by user_id;

Then if you want to get the total video_ids then you will wrap this inside of a subquery:

select sum(cnt) TotalVideos
from
(
  select user_id, count(distinct video_id) cnt
  from data
  group by user_id
) d

See SQL Fiddle with Demo of both.

The first query will give you the result of 2 for each user_id and then to get the total of all distinct video_ids you sum the count.

Answer 2

select user_id, count(distinct video_id) from TABLE group by user_id;

Answer 3

For total count...

select distinct count(video_id) from Table
where...
group...

Answer 4

现在，可以使用以下查询计算唯一user_id，video_id对的总计数

select count(distinct user_id, video_id) from table;