我需要一些查询帮助。
我有这个简单的表格:
CREATE TABLE `consecutiv` (
`id` int(11) NOT NULL auto_increment,
`readVal` int(11) default NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=16 DEFAULT CHARSET=latin1;
insert into `consecutiv`(`id`,`readVal`) values (1,2),(2,2),(3,2),(5,3),(6,3),(7,3),(8,3),(9,4),(10,5),(11,6),(12,6),(13,2),(14,2),(15,6);
看起来像这样:
id readVal
1 2
2 2
3 2
5 3
6 3
7 3
8 3
9 4
10 5
11 6
12 6
13 2
14 2
15 6
我想获得给定的readVal最后一行:
在上面的示例中将是:
id:3表示readVal = 2
id:8表示readVal = 3
...
我尝试了这个查询:
SELECT consecutiv.id, consecutiv.readVal, c.id, c.readVal FROM consecutiv
JOIN consecutiv c ON consecutiv.id = c.id-1
WHERE consecutiv.readVal!=c.readVal ORDER BY consecutiv.id ASC
只要系列中没有丢失的id,它就能正常工作。在上面的示例中,id no 4缺失,查询不会返回预期的结果。
谢谢!
答案 0 :(得分:3)
SELECT a.id, a.readVal
FROM consecutiv a
WHERE a.readVal !=
(SELECT b.readVal
FROM consecutiv b
WHERE b.id > a.id
ORDER BY id ASC
LIMIT 1)
ORDER BY a.id;
返回:
id | readval
----+---------
3 | 2
8 | 3
9 | 4
10 | 5
12 | 6
14 | 2
对于最后一行也是需要的情况:
SELECT c.id, c.readVal, c.nextReadVal
FROM
(SELECT
a.id, a.readVal,
(SELECT b.readVal
FROM consecutiv b
WHERE b.id > a.id
ORDER BY id ASC
LIMIT 1) AS nextReadVal
FROM consecutiv a) AS c
WHERE readVal != nextReadVal OR nextReadVal IS NULL
ORDER BY c.id;
返回:
id | readval | nextreadval
----+---------+-------------
3 | 2 | 3
8 | 3 | 4
9 | 4 | 5
10 | 5 | 6
12 | 6 | 2
14 | 2 | 6
15 | 6 |