Question

I need to query a MySQL database table that looks like this:

Bike  Owner  Date
-----------------------
1     Oscar  2014-02-02
2     Oscar  2014-02-02
3     John   2014-04-28
4     Jane   2014-05-29
2     John   2015-04-16
3     Mike   2015-06-16
1     Bob    2015-07-16
4     John   2015-08-16
2     Mike   2016-04-16
3     John   2016-04-16

It contains 4 bikes and as soon as the bike switches from owner, a new record is placed within this table. Since this table doesn't have an 'until' attribute, I am stuck creating a query that gets all the owners of all bikes at a specific date, say 2015-07-06.

Does anyone now how to do this in an easy way? I can think of ways of doing this by creating functions or temporary tables, but this seems way too far fetched for such an easy question.

Thanks!

Answer 1

一种方法使用显式join和聚合：

select b.*
from (select bike, max(date) as maxdate
      from bikes b
      where date <= '2015-07-06
      group by bike
     ) bd join
     bikes b
     on b.bike = bd.bike and b.date = bd.maxdate;

写一个更简短的方法：

select b.*
from bikes b
where b.date = (select max(b2.date) from bikes b2 where b2.bike = b.bike);

Answer 2

如果我正确理解了您的要求，那么这是非常直接的前言查询，让所有车主在特定日期获取

select b.*
from bikes b
where CAST(b.date AS DATE) = '2015-07-06'

Querying table with dates in SQL

2 个答案: