注意:我正在尝试学习窗口函数,所以当我可以使用GROUP BY执行此操作时 - 我明确地开始使用窗口函数
我有以下测试结果表
| 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 |
我不明白为什么这个查询,而不是使用FIRST_VALUE,我使用LAST_VALUE并相应地排序,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。
答案 0 :(得分:5)
尝试添加:
OVER (PARTITION BY TestId ORDER BY TestedOn
ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
我认为升序窗口函数的默认值是:
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
https://docs.microsoft.com/en-us/sql/t-sql/queries/select-over-clause-transact-sql
答案 1 :(得分:0)
你可以使用with子句,
的行WITH N(TESTID,LATEST_DATE) AS
(SELECT DISTINCT TestId, Max(TestedOn ) OVER(PARTITION BY TestId) FROM TestResult)
Select TestId, ResultId from FROM TestResult TR join N ON TR.TestId = N.TESTID AND TR.TestedOn =N.LATEST_DATE
表'N'只是一个临时表,其中包含TestID和LATEST_DATE
列表