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mysql join table - selecting the newest row

开发者 https://www.devze.com 2023-01-31 10:15 出处:网络
I have the following two MySQL tables TABLE NAMES NAME_IDNAME 1name1 2name2 3name3 TABLE STATUS STATUS_IDNAME_IDTIMESTAMP

I have the following two MySQL tables

TABLE NAMES

NAME_ID   NAME
1         name1
2         name2
3         name3

TABLE STATUS

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

I would like to select all info from table NAMES and add most recent correspondent TIMESTAMP column from table STATUS

RESULT

NAME_ID NAME     TIMESTA开发者_如何学运维MP
1       name1    2010-12-20 12:00
2       name2    2010-12-20 10:00
3       name3    2010-12-20 14:00

Am stuck on this one. How do I left join only on the newer timestamp?


try this query :

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


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
        )

This will handle duplicates correctly.

Create an index on table_status (name_id, timestamp, status_id) for this to work fast.


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);
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