Lead 函数在列值发生变化时取值

Question

如何编写 LEAD 函数以在 Type 发生变化时获取下一条记录的值。

源数据

Person    Type     dt_eff
123       ABC      2018-10-23
123       DEF      2018-12-19
124       ABC      2020-01-01
124       ABC      2020-02-15
124       ABC      2020-05-14
124       DEF      2020-10-13
124       FGD      2021-01-15

预期产出

Person    Type     Start_date   End_Date
123       ABC      2018-10-23   2018-12-19
123       DEF      2018-12-19   NULL
124       ABC      2020-01-01   2020-10-13
124       ABC      2020-02-15   2020-10-13
124       ABC      2020-05-14   2020-10-13
124       DEF      2020-10-13   2021-01-15
124       FGD      2021-01-15   NULL

下面的查询仅给出下一列值，但需要类型更改时记录的值。

SELECT Person, Type, dt_eff as start_date,
LEAD(dt_eff,1) over (partition by person order by dt_eff) as end_Date
FROM Person

Answer 1

您停止得太早了，在获取

lead

值后，您需要获取

max

分区上的

Person, Type

值，例如

with cte as (
  select *
    , lead(dt_eff) over (partition by Person order by Type, dt_eff) dt_eff_lead
  from Person
)
select Person, Type, dt_eff StartDate
  , max(dt_eff_lead) over (partition by Person, Type) EndDate
from cte
order by Person, Type, dt_eff;

按要求退货：

人	类型	开始日期	结束日期
123	ABC	2018-10-23	2018-12-19
123	防御	2018-12-19	空
124	ABC	2020-01-01	2020-10-13
124	ABC	2020-02-15	2020-10-13
124	ABC	2020-05-14	2020-10-13
124	防御	2020-10-13	2021-01-15
124	烟气脱硫	2021-01-15	空

DBFiddle