MySQL Query根据带有限制的条件查找行重复项

Question

I have two tables:

Members:

id     username    


Trips:

id    member_id     flag_status         created
                  ("YES" or "NO")

I can do a query like this:

SELECT 
  Trip.id, Trip.member_id, Trip.flag_status
FROM  
  trips Trip
WHERE   
  Trip.member_id = 1711
ORDER BY
  Trip.created DESC
LIMIT
  3

Which CAN give results like this:

id       member_id     flag_status
8        1711          YES
9        1711          YES
10       1711          YES

My goal is to know if the member's last three trips all had a flag_status = "YES", if any of the three != "YES", then I don't want it to count.

I also want to be able to remove the WHERE Trip.member_id = 1711 clause, and have it run for all my members, and give me the total number of members whose last 3 trips all have flag_status = "YES"

Any ideas?

Thanks!

http://sqlfiddle.com/#!2/28b2d

In that sqlfiddle, when the correct query i'm seeking runs, I should see results such as:

 COUNT(Member.id)
        2

The two members that should qualify are members 1 and 3. Member 5 fails because one of his trips has flag_status = "NO"

Answer 1

You could use GROUP_CONCAT function, to obtain a list of all of the status ordered by id in ascending order:

SELECT
  member_id,
  GROUP_CONCAT(flag_status ORDER BY id DESC) as status
FROM
  trips
GROUP BY
  member_id
HAVING
  SUBSTRING_INDEX(status, ',', 3) NOT LIKE '%NO%'

and then using SUBSTRING_INDEX you can extract only the last three status flags, and exclude those that contains a NO. Please see fiddle here . I'm assuming that all of your rows are ordered by ID, but if you have a created date you should better use:

GROUP_CONCAT(flag_status ORDER BY created DESC) as status

as Raymond suggested. Then, you could also return just the count of the rows returned using something like:

SELECT COUNT(*)
FROM (
  ...the query above...
) as q

Answer 2

Although I like the simplicity of fthiella's solution, I just can't think of a solution that depends so much on data representation. In order not to depend on it you can do something like this:

SELECT COUNT(*) FROM (
  SELECT member_id FROM (
    SELECT
      flag_status,
      @flag_index := IF(member_id = @member, @flag_index + 1, 1) flag_index,
      @member := member_id member_id
    FROM trips, (SELECT @member := 0, @flag_index := 1) init
    ORDER BY member_id, id DESC
  ) x
  WHERE flag_index <= 3
  GROUP BY member_id
  HAVING SUM(flag_status = 'NO') = 0
) x

Fiddle here . Note I've slightly modified the fiddle to remove one of the users.

The process basically ranks the trips for each of the members based on their id desc and then only keeps the last 3 of them. Then it makes sure that none of the fetched trips has a NO in the flag_status. FInally all the matching meembers are counted.