SELECT full_name,substring_index(group_concat(id ORDER BY id DESC),",",1) AS id FROM bzyd_perf_result GROUP BY full_name;
如下表：
代碼如下
CREATE TABLE `t1` (
`userid` INT(11) DEFAULT NULL,
`atime` datetime DEFAULT NULL,
KEY `idx_userid` (`userid`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8；
數據如下：
代碼如下
MySQL> SELECT * FROM t1;
+--------+---------------------+
| userid | atime |
+--------+---------------------+
| 1 | 2013-08-12 11:05:25 |
| 2 | 2013-08-12 11:05:29 |
| 3 | 2013-08-12 11:05:32 |
| 5 | 2013-08-12 11:05:34 |
| 1 | 2013-08-12 11:05:40 |
| 2 | 2013-08-12 11:05:43 |
| 3 | 2013-08-12 11:05:48 |
| 5 | 2013-08-12 11:06:03 |
+--------+---------------------+
8 ROWS IN SET (0.00 sec)
其中userid不唯一，要求取表中每個userid對應的時間離現在最近的一條記錄．初看到一個這條件一般都會想到借用臨時表及添加主建借助於join操作之類的．
給一個簡方法：
代碼如下
MySQL> SELECT userid,substring_index(group_concat(atime ORDER BY atime DESC),",",1) AS atime FROM t1 GROUP BY userid;
+--------+---------------------+
| userid | atime |
+--------+---------------------+
| 1 | 2013-08-12 11:05:40 |
| 2 | 2013-08-12 11:05:43 |
| 3 | 2013-08-12 11:05:48 |
| 5 | 2013-08-12 11:06:03 |
+--------+---------------------+
4 ROWS IN SET (0.03 sec)
查詢及刪除重復記錄
刪除表中多余的重復記錄，重復記錄是根據單個字段(peopleId)來判斷，只留有rowid最小的記錄
代碼如下
delete from people
where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1)
3、查找表中多余的重復記錄(多個字段)
代碼如下
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
4、刪除表中多余的重復記錄(多個字段)，只留有rowid最小的記錄
代碼如下
delete from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
5、查找表中多余的重復記錄(多個字段)，不包含rowid最小的記錄
代碼如下
select * from vitae a
where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1)
————————————————
版權聲明：本文為CSDN博主「歐皇·諸葛鶯」的原創文章，遵循CC 4.0 BY-SA版權協議，轉載請附上原文出處鏈接及本聲明。
原文鏈接：https://blog.csdn.net/weixin_29560137/article/details/113234203