Question

我有以下两个MySQL表

TABLE NAMES

NAME_ID   NAME
1         name1
2         name2
3         name3

表状态

STATUS_ID    NAME_ID     TIMESTAMP
1            1           2010-12-20 12:00
2            2           2010-12-20 10:00
3            3           2010-12-20 10:30
4            3           2010-12-20 14:00

我想从表格 NAMES 中选择所有信息，并从表格状态

中添加最近的通讯 TIMESTAMP 列

RESULT

NAME_ID NAME     TIMESTAMP
1       name1    2010-12-20 12:00
2       name2    2010-12-20 10:00
3       name3    2010-12-20 14:00

我坚持这个。如何仅在较新的时间戳上离开？

Answer 1

尝试此查询：

select n.NAME_ID ,  n.NAME , max(TIMESTAMP) as time from NAMES n left join 
STATUS s on s.NAME_ID = n.NAME_ID group by n.NAME_ID

Answer 2

SELECT  *
FROM    table_names tn
LEFT JOIN
        table_status ts
ON      ts.status_id = 
        (
        SELECT  status_id
        FROM    table_status tsi
        WHERE   tsi.name_id = tn.name_id
        ORDER BY
                name_id DESC, TIMESTAMP DESC, status_id DESC
        LIMIT 1
        )

这将正确处理重复。

在table_status (name_id, timestamp, status_id)上创建一个索引，以便快速工作。

Answer 3

SELECT
    status.*
FROM
    status
        JOIN
            (SELECT name_id, MAX(timestamp)AS latest FROM status GROUP BY name_id) AS sub 
            ON (status.name_id = sub.name_id AND status.timestamp = sub.latest);

mysql连接表 - 选择最新的行

3 个答案: