注意:我正在尝试学习窗口函数,因此虽然我可以使用 GROUP BY 来完成此操作 - 我明确打算使用窗口函数
我有下面的测试结果表
| Id | TargetId | TestId | ResultId | TestedOn |
+----+----------+--------+----------+--------------------------+
| 1 | 1 | 1 | 5 | 9/1/2017 6:28:32.220 PM |
| 2 | 1 | 2 | 5 | 9/1/2017 6:28:32.220 PM |
| 3 | 1 | 3 | 5 | 9/1/2017 6:28:32.220 PM |
| 4 | 1 | 1 | 4 | 9/10/2017 6:28:32.220 PM |
| 5 | 1 | 2 | 4 | 9/10/2017 6:28:32.220 PM |
| 6 | 1 | 3 | 5 | 9/10/2017 6:28:32.220 PM |
我想为每个测试 ID 选择最新结果 - 所以我有以下内容:
SELECT DISTINCT
TargetId,
TestId,
FIRST_VALUE(tr.ResultId) OVER (PARTITION BY TestId ORDER BY TestedOn DESC) LatestResultId
FROM
TestResult tr
我得到了预期的结果
| TargetId | TestId | LatestResultId |
+----------+--------+----------------+
| 1 | 1 | 4 |
| 1 | 2 | 4 |
| 1 | 3 | 5 |
我不明白的是为什么这个查询,我不使用 FIRST_VALUE,而是使用 LAST_VALUE 并进行相应排序,但这会产生不同的结果。
SELECT DISTINCT
TargetId,
TestId,
LAST_VALUE(tr.ResultId) OVER (PARTITION BY TestId ORDER BY TestedOn) LatestResultId
FROM
TestResult tr
| TargetId | TestId | LatestResultId |
+----------+--------+----------------+
| 1 | 1 | 4 |
| 1 | 1 | 5 |
| 1 | 2 | 4 |
| 1 | 2 | 5 |
| 1 | 3 | 5 |
| 1 | 3 | 5 |
对我来说,这些查询应该产生相同的结果集。
最佳答案
尝试添加:
OVER (PARTITION BY TestId ORDER BY TestedOn
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
我相信升序窗口函数的默认值是:
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
https://learn.microsoft.com/en-us/sql/t-sql/queries/select-over-clause-transact-sql
关于sql - 通过 SQL PARTITION 选择最新项目,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46351176/