如果可以更改表的结构，建议更改分类表以包括结束日期和开始日期-这样将更容易加入表。
如果没有，我建议如下：
SELECt case.id, case.resolution, case.timestamp, class.value FROM closed_cases AS case LEFT JOIN (select c.*, (select min(timestamp) from classifications c1where c1.timestamp > c.timestamp) timeend from classifications c) AS class ON case.timestamp >= class.timestamp and (case.timestamp < class.timeend or class.timeend IS NULL) WHERe case.timestamp BETWEEN $1 AND $2;
编辑-结束日期为分类：
SELECt case.id, case.resolution, case.timestamp, class.value FROM closed_cases AS case LEFT JOIN classifications AS class ON case.timestamp >= class.timestamp and case.timestamp < class.timeend WHERe case.timestamp BETWEEN $1 AND $2;
