[英]mySQL - select the top n rows, grouped by 2 columns
我已經找到了現有的問題,包括幾個字段的最新/最低單行,或單個字段上的最新n行,但不是兩個在一起
我需要構建2個查詢,使用此示例表(類似於此問題 )
CREATE TABLElap_data
(id
int(1) NOT NULL,track_id
int(1) NOT NULL,user_id
int(1) NOT NULL,lap_time
time NOT NULL,lap_status
tinyint(1) NOT NULL, PRIMARY KEY (id
) ) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;
INSERT INTO `lap_data` (`id`, `track_id`, `user_id`, `lap_time`, `lap_status`) VALUES (1, 1, 1, '04:18:23', 1), (2, 2, 2, '01:09:54', 1), (3, 2, 1, '01:05:30', 1), (4, 1, 2, '04:17:02', 1), (5, 3, 2, '01:13:10', 1), (6, 4, 1, '01:36:59', 0), (7, 3, 2, '01:18:10', 1), (8, 2, 3, '01:06:42', 1), (9, 1, 1, '04:16:12', 1), (10, 1, 2, '04:18:12', 1), (11, 2, 3, '01:03:20', 1), (12, 2, 1, '01:08:13', 1), (13, 2, 1, '01:09:44', 1), (14, 3, 2, '01:14:10', 1), (15, 3, 2, '01:17:20', 1), (16, 4, 1, '01:36:23', 1), (17, 2, 1, '01:11:34', 1);
查詢1:
這是我在其他地方用來收集給定類型的兩個最新記錄的查詢,這個記錄最接近我認為我需要的,修改為這個例子..雖然未完成,但在另一個例子中,它只是收集每個user_id的2個最新行..在這里我需要它也考慮到track_id
SELECT
*
FROM (
SELECT
t.id,
t.track_id,
t.user_id,
t.lap_time,
t.lap_status,
@row:=case WHEN @prev=user_id THEN @row ELSE 0 END +1 rn,
@prev:=user_id
FROM `lap_data` t
CROSS JOIN (SELECT @row:=0, @prev:=null) c
WHERE t.user_id IN (1,2)
ORDER BY user_id, id DESC
) src
WHERE rn <= 2
ORDER BY lap_time DESC
查詢1所需結果: (WHERE user_id IN(1,2))
| id | track_id | user_id | lap_time | lap_status | -------------------------------------------------------------- | 9 | 1 | 1 | 04:16:12 | 1 | | 1 | 1 | 1 | 04:18:23 | 1 | | 3 | 2 | 1 | 01:05:30 | 1 | | 12 | 2 | 1 | 01:08:13 | 1 | | 16 | 4 | 1 | 01:36:23 | 1 | | 6 | 4 | 1 | 01:36:59 | 1 | | 4 | 1 | 2 | 04:17:02 | 1 | | 10 | 1 | 2 | 04:18:12 | 1 | | 2 | 2 | 2 | 01:09:54 | 1 | | 5 | 3 | 2 | 01:13:10 | 1 | | 14 | 3 | 2 | 01:14:10 | 1 |
查詢2:
查詢2所需結果: (WHERE user_id ='1')
| id | track_id | user_id | lap_time | lap_status | -------------------------------------------------------------- | 13 | 2 | 1 | 01:09:44 | 1 | | 17 | 2 | 1 | 01:11:34 | 1 |
有什么建議么? 謝謝!
我之前回答的MYSQL版本:
SELECT
lt.id,
lt.user_id,
lt.track_id,
lt.lap_status,
lt.lap_time
FROM (
SELECT id,
user_id,
track_id,
lap_status,
lap_time,
CASE WHEN track_id = @prevTrackId AND user_id = @prevUserId THEN @curRank := @curRank + 1 ELSE @curRank := 1 END Rank,
@prevTrackId := track_id,
@prevUserId := user_id
FROM lap_data, (SELECT @curRank := 0, @prevTrackId := 1, @prevUserId := 1) r
ORDER BY user_id,track_id,lap_time ASC
) lt
WHERE Rank <= 2
該查詢產生一個重要的(並且很可能是錯誤的)假設 - 即先前用戶的最高track_id高於(或至少不同)后續用戶的最低track_id。
如果不是這種情況,那么您可能需要存儲另一個變量,或者將“prev”基於兩個值的串聯...
SELECT x.id
, x.track_id
, x.user_id
, x.lap_time
, x.lap_status
FROM
( SELECT l.*
, CASE WHEN @prev = track_id THEN @i:=@i+1 ELSE @i:=1 END rank
, @prev:=track_id prev
FROM lap_data l
, (SELECT @prev:=null,@i:=0) vars
WHERE user_id IN(1,2)
ORDER
BY user_id
, track_id
, lap_time
) x
WHERE x.rank <=2
ORDER
BY user_id
, track_id
, lap_time;
select id,track_id,user_id,lap_status,lap_time from (
select @rank:=if(@prev_cat=user_id,@rank+1,1) as rank,id,user_id,track_id,lap_status,lap_time,@prev_cat:=user_id
from lap_data,(select @rank:=0, @prev_cat:="")t
where user_id IN(1,2) order by track_id, user_id desc
) temp
where temp.rank<=2
查詢1:
SELECT lt.id,lt.user_id,lt.track_id,lt.lap_status,lt.lap_time
FROM (
SELECT id,user_id,track_id,lap_status,lap_time,Rank()
over (Partition BY user_id,track_id
ORDER BY lap_time ASC ) AS Rank
FROM lap_data
WHERE user_id IN (1,2)
) lt WHERE Rank <= 2
查詢2:只需選擇NOT IN
Query 1中的所有記錄(假設id是表的主鍵,你甚至沒有為lap_data表設置主鍵)
SELECT * FROM lap_data
WHERE id NOT IN
(SELECT lt.id
FROM (
SELECT id,Rank()
over (Partition BY user_id,track_id
ORDER BY lap_time ASC ) AS Rank
FROM lap_data
WHERE user_id = 1
) lt WHERE Rank <= 2)
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