mySQL查询返回每个表的最后一条记录

Question

我有一个mySQl db(名称为"stock"),有50个表,每个表都有

id,符号,日期,时间,打开,高,低,关闭,列作为列(9列).

我想知道每张桌子的最后一张记录是什么,按日期和时间排序.

我是否必须对每个表的所有数据进行ORDER BY,或者有更好的方法来了解最后一条记录？

我正在请求帮助查询只返回db中每个表的最后一条记录.

谢谢

PS对于最后一个记录,我的意思是最近的日期然后是时间

Answer 1

有两种选择:

-- I would use this only if you need more than one records
SELECT * FROM table ORDER BY date DESC LIMIT 1;

-- Way to go:
SELECT * FROM table WHERE date = (SELECT MAX(date) FROM table) LIMIT 1;

不要忘记添加索引date.如果您可以同时添加大量记录,则必须添加:

ORDER BY id DESC -- In case that date is highest for records for last records
ORDER BY time DESC -- Every other case

到查询结束

Answer 2

我将假设具有最大ID的记录是"最后一个"(假设严格增加的表中唯一的顺序ID).如果你有一个更好的"最后"定义可能会有所作为.

要获得一个"最后"记录,您可以:

Select * from table_1 where id = (select max(id) from table_1);

要将所有50个表的结果合并到一个结果集中,您可以执行以下操作:

Select * from table_1 where id = (select max(id) from table_1)
union
Select * from table_2 where id = (select max(id) from table_2)
union
Select * from table_3 where id = (select max(id) from table_3)
union...

特定于MySQL的解决方案可能是

Select * from table_1 order by id desc limit 1
union
Select * from table_2 order by id desc limit 1
union
Select * from table_3 order by id desc limit 1
union...

根据您的编辑(您实际定义"最后"的意思):

Select * from table_1 order by date desc, time desc, id desc limit 1
union
Select * from table_2 order by date desc, time desc, id desc limit 1
union
Select * from table_3 order by date desc, time desc, id desc limit 1
union...