有没有办法强制PostgreSQL LAG()和LEAD()函数使用的值不是来自前导行而是来自同一分区的下一个等级？
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| client_id | order_id | product_id | year | rank |
---------------------------------------------------
| 1 | 1 | 111345 | 1995 | 1 |
| 1 | 1 | 912346 | 1995 | 1 |
| 1 | 1 | 212346 | 1995 | 1 |
| 1 | 2 | 233368 | 1998 | 4 |
| 1 | 2 | 133368 | 1998 | 4 |
| 1 | 3 | 412341 | 2005 | 6 |
| 2 | 55 | 312344 | 1995 | 1 |
| 2 | 57 | 812343 | 1999 | 2 |
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预期结果将是：
---------------------------------------------------------------------------
| client_id | order_id | product_id | year | rank | prev_year | next_year |
---------------------------------------------------------------------------
| 1 | 1 | 111345 | 1995 | 1 | null | 1998 |
| 1 | 1 | 912346 | 1995 | 1 | null | 1998 |
| 1 | 1 | 212346 | 1995 | 1 | null | 1998 |
| 1 | 2 | 233368 | 1998 | 4 | 1995 | 2005 |
| 1 | 2 | 133368 | 1998 | 4 | 1995 | 2005 |
| 1 | 3 | 412341 | 2005 | 6 | 1998 | null |
| 2 | 55 | 312344 | 1995 | 1 | null | 1999 |
| 2 | 57 | 812343 | 1999 | 2 | 1995 | null |
---------------------------------------------------------------------------
如果year在给定排名中具有不同的值，则prev_year和next_year可以是这些值中的任何一个。例如：
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| client_id | order_id | product_id | year | rank | prev_year | next_year |
---------------------------------------------------------------------------
| 1 | 1 | 111345 | 1994 | 1 | null | 1998 |
| 1 | 1 | 912346 | 1995 | 1 | null | 1998 |
| 1 | 1 | 212346 | 1996 | 1 | null | 1998 |
| 1 | 2 | 233368 | 1998 | 4 | ???? | null |
????可以等于1994年，1995年或1996年
答案 0 :(得分：2)
您应该对数据集使用lag()和lead()函数，每对(client_id, rank)减少为一行：
select
client_id, order_id, product_id,
t.year, rank, prev_year, next_year
from my_table t
join (
select distinct on (client_id, rank)
client_id, rank, year,
lag(year) over w as prev_year,
lead(year) over w as next_year
from my_table
window w as (partition by client_id order by rank)
order by 1, 2, 3 desc
) s using (client_id, rank)
order by client_id, rank
client_id | order_id | product_id | year | rank | prev_year | next_year
-----------+----------+------------+------+------+-----------+-----------
1 | 1 | 212346 | 1995 | 1 | | 1998
1 | 1 | 912346 | 1995 | 1 | | 1998
1 | 1 | 111345 | 1995 | 1 | | 1998
1 | 2 | 133368 | 1998 | 4 | 1995 | 2005
1 | 2 | 233368 | 1998 | 4 | 1995 | 2005
1 | 3 | 412341 | 2005 | 6 | 1998 |
2 | 55 | 312344 | 1995 | 1 | | 1999
2 | 57 | 812343 | 1999 | 2 | 1995 |
(8 rows)