Convert BigInt timestamp to a real Date with row aggregation and operations in mySQL(在 mySQL 中使用行聚合和操作将 BigInt 时间戳转换为真实日期)

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问题描述

我有一个查询，它采用上次更新日期(时间戳，但作为 bigint(20) 列)，如下所示:

I have a query which takes the last update date (timestamp but as a bigint(20) column) like this: 

SELECT a.id_workorder, MAX(b.update_date) AS udpate_date
FROM main_log a, 
(
    SELECT MAX(log_date) AS update_date, log_id 
    FROM log_a
    GROUP BY log_id
    UNION
    SELECT MAX(log_date) AS update_date, log_id 
    FROM log_b
    GROUP BY log_id
)b
WHERE a.id_log = b.log_id
GROUP BY b.log_id

并且它返回任何类型的日志(a 或 b)的最后更新日期(unix 时间戳作为 bigint(20)):

and it returns the last update date (unix timestamp as a bigint(20)) for any kind of log (a or b):

id          last update
-------------------------
1001        1376750476349
1002        1376753690861
1003        1378122801986
1004        1377764414858
1005        1377847226096
...

现在我想以日期格式格式化返回，虽然我可以像这样使用 FROM_UNIXTIME 格式化外部时间戳，但我很天真:

Now I want to format the return in date format and I naively though I can just format the outside timestamp with FROM_UNIXTIME like this:

SELECT 
    a.id_workorder, 
    FROM_UNIXTIME(MAX(b.update_date)) AS udpate_date
FROM main_log a, 
(
    SELECT MAX(log_date) AS update_date, log_id 
    FROM log_a
    GROUP BY log_id
    UNION
    SELECT MAX(log_date) AS update_date, log_id 
    FROM log_b
    GROUP BY log_id
)b
WHERE a.id_log = b.log_id
GROUP BY b.log_id

但它给了

id          last update
-------------------------
1001        null
1002        null
1003        null
1004        null
1005        null
...

我也尝试将转换放入内部查询中，但结果相同.

I tried to put the conversion in the inner queries as well but it is the same.

我还尝试在 SO、mySQL 文档和 Google 上找到答案，但没有找到为什么在我创建 group by 时转换不起作用.

I also tried to find answers on SO, mySQL documentation and Google but did not find why the conversion does not works when I make a group by.

推荐答案

您的时间戳以毫秒为单位尝试:

Your timestamp is in milliseconds try:

SELECT a.id_workorder, 
FROM_UNIXTIME(MAX(b.update_date/1000)) AS udpate_date
FROM main_log a, ...

(即时间除以 1000 得到秒)

(i.e. divide the time by 1000 to get seconds)

mysql> select FROM_UNIXTIME(1376750476349);
+------------------------------+
| FROM_UNIXTIME(1376750476349) |
+------------------------------+
| NULL                         |
+------------------------------+
1 row in set (0.06 sec)

mysql> select FROM_UNIXTIME(1376750476349/1000);
+-----------------------------------+
| FROM_UNIXTIME(1376750476349/1000) |
+-----------------------------------+
| 2013-08-17 15:41:16               |
+-----------------------------------+
1 row in set (0.02 sec)

mysql>

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