[英]mysql select latest timestamp in a group
我有一个表,我想在表中选择一个特定列的值定义的类别中的最新时间戳。
特别
SELECT *
FROM takelist
WHERE producer_name = 'sean'
AND bucket_id = '2CCEx15_1o'
结果是
+-------------+---------------+------------+---------------------+
| takelist_id | producer_name | bucket_id | ts |
+-------------+---------------+------------+---------------------+
| 1 | sean | 2CCEx15_1o | 2013-10-07 18:29:00 |
| 4 | sean | 2CCEx15_1o | 2013-10-07 18:33:09 |
| 5 | sean | 2CCEx15_1o | 2013-10-07 18:33:38 |
| 27 | sean | 2CCEx15_1o | 2013-10-07 18:37:38 |
| 212 | sean | 2CCEx15_1o | 2013-10-14 18:36:05 |
| 236 | sean | 2CCEx15_1o | 2013-10-21 17:59:56 |
| 237 | sean | 2CCEx15_1o | 2013-10-21 18:00:55 |
| 281 | sean | 2CCEx15_1o | 2013-10-29 15:58:40 |
| 287 | sean | 2CCEx15_1o | 2013-10-29 19:24:15 |
| 330 | sean | 2CCEx15_1o | 2013-10-31 14:39:33 |
| 615 | sean | 2CCEx15_1o | 2013-12-16 22:46:59 |
| 616 | sean | 2CCEx15_1o | 2013-12-16 22:54:46 |
+-------------+---------------+------------+---------------------+
我想为名为bucket_id的列的每个唯一值选择一行,其中所选行具有最新的时间戳。
我根据之前对类似问题的回答尝试过以下,但一定有错
SELECT takes.* FROM takelist as takes
INNER JOIN (
SELECT takelist_id, max(ts) max_ts, bucket_id
FROM takelist
WHERE producer_name='sean'
GROUP BY bucket_id
) latest_take
ON takes.takelist_id=latest_take.takelist_id
AND takes.ts=latest_take.max_ts
您的查询已结束。 但是您使用的是id而不是时间戳:
SELECT takes.*
FROM takelist takes INNER JOIN
(SELECT max(ts) as max_ts, bucket_id
FROM takelist
WHERE producer_name = 'sean'
GROUP BY bucket_id
) latest_take
ON takes.ts = latest_take.max_ts and takes.bucket_id = latest_take.bucket_id;
在原始公式中选择任意takelist_id
。 它可能不是你想要的那个。
尝试这个:
SELECT t.*
FROM takelist AS t
INNER JOIN (SELECT MAX(ts) max_ts, bucket_id
FROM takelist WHERE producer_name='sean'
GROUP BY bucket_id
) lt ON t.bucket_id=lt.bucket_id AND t.ts=lt.max_ts;
要么
SELECT *
FROM (SELECT * FROM takelist WHERE producer_name='sean' ORDER BY bucket_id, ts DESC) A
GROUP BY bucket_id
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