SQL：如何根据上一行更新一行

Question

我有下表：

id-家庭ID-家庭状态-以前的家庭状态

1  - a - occupied - null

2  - a - abandoned - null 

3  - a - foreclosure - null 

4  - b - occupied - null  

5  - b - occupied - null 

6  - c - occupied - null 

我想生成一条更新语句，该语句将表更新如下：

1  - a - occupied - abandoned

2  - a - abandoned - foreclosure 

3  - a - foreclosure - null 

4  - b - occupied - occupied  

5  - b - occupied - null 

6  - c - occupied - null

我正在使用以下算法：

set @id = 1
set @max_id = (select MAX(id) from home)

select @homeid = homeid from home where id = @id

while @id <= @max_id
begin

     select 
        @previous_homeid = home,
        @previous_home_status = @home_status
    from 
        home where id = (@id + 1)

    if(@previous_homeid = @homeid)
    begin
        update 
            home 
        set  
            home_status = @previous_home_status
        where 
            id = @id
    end

    set @homeid = @previous_homeid
    set @previous_homeid = null
    set @previous_home_status = null
    set @id = @id + 1;
end

有没有更有效的算法？ 我不喜欢循环效率

Answer 1

您可以使用lead获取下一行的值。

with cte as (select t.*
             ,lead(home_status) over(partition by home_id order by id) as next_home_status
             from tbl t)
update cte set previous_home_status=next_home_status

Answer 2

这未经测试，但是应该可以帮助您：

WITH CTE AS(
    SELECT id, [home id], [home status], [previous home status],
           LEAD([previous home status]) OVER (PARTITION BY [home id] ORDER BY id ASC) AS NextStatus
    FROM home)
UPDATE CTE
SET [previous home status] = NextStatus;