递归 CTE 存在性能问题，需要建议优化查询

Question

我想从日志表中获取前 5 条记录，其中"批准日期"像 NULL 一样更改为值，反之亦然。日期值无关紧要，但顺序很重要。

ApprovedDate            ChangeDate                         changeByUser
NULL                    2019-12-09 06:40:15.437              vaisakh
NULL                    2019-12-09 06:42:31.563             vaisakh
NULL                    2019-12-09 06:42:33.140             vaisakh
NULL                    2019-12-09 07:03:54.660              vaisakh
2019-12-09 07:05:29.800 2019-12-09 07:05:29.817              vaisakh
2019-12-09 07:05:29.800 2019-12-09 07:05:38.707              vaisakh
NULL                    2019-12-09 07:09:33.160               vaisakh
NULL                    2019-12-09 07:09:42.440               vaisakh
NULL                    2019-12-09 09:38:19.757             vaisakh
2019-12-09 09:41:42.977 2019-12-09 09:41:43.243             Raveendran        

在这种情况下，我想要第一条记录和第 5 条记录(有人批准了数据，这就是为什么一个值(，然后第 7 条记录值为空，有人拒绝了它。

我尝试使用递归 CTE 它正在工作，但对于大型记录来说，巨大的性能问题

DECLARE @today DATETIME = GETDATE();
with RESULT (CIPApprovedDate,ChangeDate,changeByUser,legalId,depth)AS(
SELECT TOP 1 CIPApprovedDate, ChangeDate, changeByUser, legalId,1
FROM LegalEntityExtensionLog
WHERE legalId= 2688518
ORDER BY ChangeDate ASC
union ALL
select 
L.CIPApprovedDate, L.ChangeDate, L.changeByUser, L.legalId,ct.depth+1
FROM LegalEntityExtensionLog L INNER JOIN Result CT
on L.legalId=CT.legalId AND L.changeDate>CT.changeDate
AND ISNULL(L.CIPApprovedDate,@today) <> ISNULL(CT.CIPApprovedDate,@today) 
)select * from Log  where  ChangeDate in(select MIN(ChangeDate) from Result group by depth)

Answer 1

您可以像这样提取转换记录：

select ApprovedDate, ChangeDate, changeByUser
from (
select 
l.*,
lag(ApprovedDate) ver(partition by LegalId order by ChangeDate) lagApprovedDate
from LegalEntityExtensionLog l
) t
where 
(lagApprovedDate is null and ApprovedDate is not null)
or (lagApprovedDate is not null and ApprovedDate is null)

这将显示ApprovedDate从null转换为非null值(或相反(的记录。

Answer 2

递归 CTE 通过每次递归访问表有时可能会很慢。

但是是否需要获得空/非空开关？

这将得到相同的结果

-- Sample data
CREATE TABLE LegalEntityExtensionLog
(
Id int identity(1,1) primary key,
ApprovedDate datetime, 
ChangeDate datetime not null, 
ChangeByUser varchar(42) not null, 
LegalId int not null
);
insert into LegalEntityExtensionLog
(ApprovedDate, ChangeDate, ChangeByUser, LegalId) values
(NULL,                      '2019-12-09 06:40:15.437', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 06:42:31.563', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 06:42:33.140', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 07:03:54.660', 'vaisakh', 2688518)
,('2019-12-09 07:05:29.800', '2019-12-09 07:05:29.817', 'vaisakh', 2688518)
,('2019-12-09 07:05:29.800', '2019-12-09 07:05:38.707', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 07:09:33.160', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 07:09:42.440', 'vaisakh', 2688518)
,(NULL,                      '2019-12-09 09:38:19.757', 'vaisakh', 2688518)
,('2019-12-09 09:41:42.977', '2019-12-09 09:41:43.243', 'Raveendran', 2688518)
;

查询：

WITH RESULT AS
(
SELECT *
, ROW_NUMBER() OVER (PARTITION BY LegalId ORDER BY ChangeDate) AS rn
, LAG(ApprovedDate) OVER (PARTITION BY LegalId ORDER BY ChangeDate) AS prevApprDt
FROM LegalEntityExtensionLog
WHERE legalId = 2688518
AND ChangeDate >= cast('2019-12-09' AS DATE)
)
SELECT ApprovedDate, ChangeDate, ChangeByUser, LegalId
FROM RESULT
WHERE 
( RN = 1
OR (ApprovedDate IS NULL AND prevApprDt IS NOT NULL)
OR (ApprovedDate IS NOT NULL AND prevApprDt IS NULL)
)
ORDER BY ChangeDate
GO

结果：

批准日期 |变更日期 |更改用户 |合法身份证 :------------------ |:------------------ |:----------- |------:空|2019-09-12 06：40：15 |维萨克 |2688518 2019-09-12 07：05：29 |2019-09-12 07：05：29 |维萨克 |2688518空|2019/09/12 07：09：33 |维萨克 |2688518 2019-09-12 09：41：42 |2019-09-12 09：41：43 |拉文德兰 |2688518

数据库<>在这里小提琴