Question

我遇到以下SQL查询和MySQL

的问题

SELECT
  id, cpid, label, cpdatetime
FROM
  mytable AS a
WHERE
  id NOT IN
  (
    SELECT
      id
    FROM
      mytable AS b
    WHERE
      a.label = b.label
    AND
      a.cpdatetime > b.cpdatetime
  )
AND
  label LIKE 'CB%'
AND
  cpid LIKE :cpid
GROUP BY label
ORDER BY cpdatetime ASC

表格如下所示

1 | 170.1 | CB55 | 2013-01-01 00:00:01
2 | 135.5 | CB55 | 2013-01-01 00:00:02
3 | 135.6 | CB59 | 2013-01-01 00:00:03
4 | 135.5 | CM43 | 2013-01-01 00:00:04
5 | 135.5 | CB46 | 2013-01-01 00:00:05
6 | 135.7 | CB46 | 2013-01-01 00:00:06
7 | 170.2 | CB46 | 2013-01-01 00:00:07

我希望我的查询返回

3 | 135.6 | CB59
5 | 135.5 | CB46

修改

标签是狗/猫，而cpids是保持狗/猫的临时家庭。

狗/猫从一个家庭搬到另一个家庭。

我需要找到位于：userinput系列中的狗/猫，但前提是他们不在另一个家庭中

我无法改变数据库，只需按原样处理数据，而我不是编写应用程序/数据库模式的人。

Answer 1

尝试使用LEFT JOIN

来避免相关的子查询

SELECT a.id, a.cpid, a.label, a.cpdatetime
FROM mytable AS a
LEFT JOIN mytable AS b ON a.label = b.label AND a.cpdatetime > b.cpdatetime
WHERE a.label LIKE 'CB%' AND a.cpid LIKE :cpid
  AND b.label IS NULL
GROUP BY a.label
ORDER BY a.cpdatetime ASC

Fiddle

如果联接条件失败，则第二个表别名b的字段将设置为NULL。

或者，使用非相关子查询：

SELECT a.id, a.cpid, a.label, a.cpdatetime
FROM mytable AS a
INNER JOIN (
  SELECT label, MIN(cpdatetime) AS cpdatetime
  FROM mytable
  WHERE label LIKE 'CB%'
  GROUP BY label
) AS b ON a.label = b.label AND a.cpdatetime = b.cpdatetime
WHERE a.cpid LIKE '135%'
ORDER BY a.cpdatetime

首先，您会找到每个标签的最小cpdatetime，然后将其与添加了cpid条件的第一个表连接起来。

Answer 2

我认为这就是你想要做的 - 选择每个标签最早ID的ID，然后选择带有135 cpid和CB标签的记录。

SELECT
  A.id, cpid, A.label, cpdatetime
FROM
  mytable AS a inner join
 (select id, label from mytable
  group by label
  having min(cpdatetime)) as b
on A.label=B.label and A.id=B.id
WHERE
  A.label LIKE 'CB%'
AND
  cpid LIKE '135%'
GROUP BY A.label
ORDER BY cpdatetime ASC;

http://sqlfiddle.com/#!2/ccccf/16

SQL SELECT WHERE NOT IN来自同一个表查询

2 个答案: