Question

这是我的表（多对多的关系）。他们的目标 - 为不同的请求保留状态变化的历史记录。（我从插图中删除了对问题没有意义的所有字段）

1的请

id (primary, ai) | name (varchar) | phone (varchar) | text (varchar)

1 | Maria | 9232342323 | "fist text"
2 | Petr  | 2342342323 | "second text"
3 | Lenny | 2342342323 | "third text"

2的以下状态

id (primary, ai) | title (varchar)

1 | New
2 | In progress
3 | Abort

3的 Requests_has_Statuses

id (primary, ai) | requests_id (fk) | statuses_id (fk) | comment (varchar) | date (timestamp)

1 | 1 | 1 | "Fist comment about a Maria's request" | 2014-08-08 12:24
2 | 1 | 2 | "Second comment about Maria"           | 2014-08-08 12:26
3 | 1 | 2 | "Third comment about Maria"            | 2014-08-08 12: 57
4 | 2 | 1 | "First comment about Petr"             | 2014-08-08 13:23
5 | 3 | 1 | "First comment about Lenny"            | 2014-08-08 13:45
6 | 2 | 3 | "Second comment about Petr"            | 2014-08-08 14:00

我的目标是选择这样的输出：

1 | Maria | 9232342323 | "In progress" | "Third comment about Maria"  | 2014-08-08 12: 57
2 | Petr  | 2342342323 | "Abort"       | "Second comment about Petr"  | 2014-08-08 14:00
3 | Lenny | 2342342323 | "New"         | "First comment about Lenny"  | 2014-08-08 13:45

简单来说，我需要输出当前的实际状态和每个请求的信息。

我试图这样做：

SELECT r.name, r.phone, st.title, rhs.comment, rhs.date
FROM requests AS r
INNER JOIN Requests_has_Statuses AS rhs ON rhs.requests_id = r.id
INNER JOIN Statuses AS st ON rhs.statuses_id = st.id;

但我有一个不必要的重复，如：

1 | Maria | 9232342323 | "New"         | "Fist comment about a Maria's request"  | 2014-08-08 12:24
1 | Maria | 9232342323 | "In progress" | "Second comment about Maria"            | 2014-08-08 12: 26
1 | Maria | 9232342323 | "In progress" | "Third comment about Maria"             | 2014-08-08 12: 57
2 | Petr  | 2342342323 | "New"         | "First comment about Petr"              |2014-08-08 13:23
3 | Lenny | 2342342323 | "New"         | "First comment about Lenny"             | 2014-08-08 13:45
2 | Petr  | 2342342323 | "Abort"       | "Second comment about Petr"             | 2014-08-08 14:00

你能帮我提一些建议或解决方案吗？感谢

Answer 1

添加过滤器以仅获取每个请求者的最新状态：

SELECT r.name, r.phone, st.title, rhs.comment, rhs.date
FROM requests AS r
INNER JOIN Requests_has_Statuses AS rhs ON rhs.requests_id = r.id
INNER JOIN Statuses AS st ON rhs.statuses_id = st.id
where rhs.id in 
(select max(id)
from  Requests_has_Statuses AS rhs2
where rhs.requests_id = rhs2.requests_id
group by rhs2.requests_id
)

Answer 2

另外请尝试下一个查询，使用DISTINCT（只返回一行），最后按日期排序（ORDER BY）：

SELECT  DISTINCT r.name, r.phone, st.title, rhs.comment, rhs.date
FROM requests AS r
INNER JOIN Requests_has_Statuses AS rhs ON rhs.requests_id = r.id
INNER JOIN Statuses AS st ON rhs.statuses_id = st.id
ORDER BY rhs.date DESC;

Answer 3

在编写交叉表计算时，我从不使用JOIN。试试这个，

SELECT name, phone, title, comment, date , requests_id , title
FROM Requests Statuses Requests_has_Statuses
Where Requests.id=Statuses.id AND Requests.id=Requests_has_Statuses.id

<强> 修改

GROUP BY name;

Answer 4

试试这个：

SELECT r.id, r.phone, st.title, rhs.comment, rhs.date
FROM (
    SELECT r.id, max(rhs.date) AS date
    FROM Requests_has_Statuses AS rhs
    INNER JOIN Requests r ON r.id = rhs.requestId
    GROUP BY r.id) AS temp
INNER JOIN Requests AS r ON temp.id = r.id
INNER JOIN Requests_has_Statuses AS rhs ON rhs.requestId = temp.id and rhs.date = temp.date
INNER JOIN Statuses AS st ON rhs.statusId = st.id

如何避免下面的mysql查询中的重复行情况？

4 个答案: