使用mySQL中的行聚合和操作将BigInt时间戳转换为实际日期

Question

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:

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)):

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

现在我想格式化日期格式的返回,我天真地虽然我可以FROM_UNIXTIME像这样格式化外部时间戳:

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
...

我试图将转换放在内部查询中,但它是相同的.

我也尝试在SO,mySQL文档和谷歌上找到答案但是没有找到为什么转换在我制作时不起作用group by.

Answer 1

您的时间戳以毫秒为单位尝试:

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

(即将时间除以1000得秒)

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>