游戏MySQL表：如何仅计算每个用户的首次尝试并提供正确/不正确的总和？

Question

I have created a game where users can answer quiz questions - as many times as they want. See example question here (stats are in the sidebar top right).

Currently I am only counting the total statistics, ie all attempts of all users. This, of course, is falsifying the per question statistics.

SELECT SUM(correct=1) AS correct, SUM(correct=0) AS incorrect, timestamp 
    FROM `gametable` 
    WHERE questionid = #

Example date for the gametable:

+---------------------+--------+------------+---------+
| timestamp           | userid | questionid | correct |
+---------------------+--------+------------+---------+
| 2014-12-07 15:38:35 |      1 |         33 |       0 |
| 2014-12-07 15:39:40 |      1 |         33 |       1 |
| 2014-12-07 15:41:40 |      1 |         33 |       1 |
| 2014-12-07 16:00:17 |      2 |         33 |       1 |
| 2014-12-07 16:08:00 |      2 |         33 |       0 |
| 2014-12-07 16:09:00 |      2 |         33 |       0 |
| 2014-12-07 16:10:25 |      2 |         33 |       1 |
+---------------------+--------+------------+---------+

The result for the above table with the mysql query given would be: 4 correct and 3 incorrect.

However, the "first attempt" result should be: 1 correct and 1 incorrect .

Is there a way to write a mysql query to do this?

Answer 1

Using a sub query to get the first attempt for each user:-

SELECT SUM(correct=1) AS correct, SUM(correct=0) AS incorrect
FROM `gametable` 
INNER JOIN
(
    SELECT userid, MIN(timestamp) AS mintimestamp
    FROM `gametable` 
    GROUP BY userid
) sub0
ON gametable.userid = sub0.userid
WHERE questionid = #
AND gametable.timestamp =  sub0.mintimestamp

Note I have removed the timestamp column from your outer select as it didn't appear to be required, nor would it bring back a meaningful value.

Note that your sample data doesn't include a question field, but your example SQL does. Assuming you do have a question field you would need to select the first attempt for the particular question as well:-

SELECT SUM(correct=1) AS correct, SUM(correct=0) AS incorrect
FROM `gametable` 
INNER JOIN
(
    SELECT userid, questionid, MIN(timestamp) AS mintimestamp
    FROM `gametable` 
    GROUP BY userid, questionid
) sub0
ON gametable.userid = sub0.userid
AND gametable.questionid = sub0.questionid
AND gametable.timestamp =  sub0.mintimestamp
WHERE gametable.questionid = #

or

SELECT SUM(correct=1) AS correct, SUM(correct=0) AS incorrect
FROM `gametable` 
INNER JOIN
(
    SELECT userid, MIN(timestamp) AS mintimestamp
    FROM `gametable` 
    WHERE gametable.questionid = #
    GROUP BY userid
) sub0
ON gametable.userid = sub0.userid
AND gametable.timestamp =  sub0.mintimestamp

EDIT - Suggestion to cope with anonymous users based on a cookie id. This is returning the cookie id if the user id is null, otherwise it is returning null for the cookie id. Done like this so that the cookie id is ignored for records with a user id.

SELECT SUM(correct=1) AS correct, SUM(correct=0) AS incorrect
FROM `gametable` 
INNER JOIN
(
    SELECT userid, if(userid IS NULL, cookie_id, NULL) AS cookie_id, questionid, MIN(timestamp) AS mintimestamp
    FROM `gametable` 
    GROUP BY userid, cookie_id, questionid
) sub0
ON ((gametable.userid IS NULL
AND gametable.cookie_id = sub0.cookie_id)
OR (gametable.userid IS NOT NULL
AND gametable.userid = sub0.userid))
AND gametable.questionid = sub0.questionid
AND gametable.timestamp =  sub0.mintimestamp
WHERE gametable.questionid = #