SQL 如何在不使用超前和滞后的情况下更新上一行和下一行的值？

Question

我正在尝试根据 aa 列中的值标记一些行，但我还需要根据当前行值为上一行和下一行放置相同的标志。

所以下面是我的桌子

-- create a table
CREATE TABLE table1 (
  id INTEGER PRIMARY KEY,
  time INTEGER,
  event varchar NOT NULL
  );
-- insert some values
INSERT INTO table1 VALUES (1, '1', 'r');
INSERT INTO table1 VALUES (2, '2', 'r');
INSERT INTO table1 VALUES (3, '3', 's');
INSERT INTO table1 VALUES (4, '4', 'r');
INSERT INTO table1 VALUES (5, '5', 'r');
INSERT INTO table1 VALUES (6, '6', 'r');
INSERT INTO table1 VALUES (7, '7', 's');
INSERT INTO table1 VALUES (8, '8', 'r');
INSERT INTO table1 VALUES (9, '9', 'r');
INSERT INTO table1 VALUES (10, '10', 's');

我想为event='s'添加一个包含0的列flag ，以及它的上一行和下一行。 但由于系统限制，不能使用lead或lag或临时表。

所以我最终的 output 看起来像这样

+-----------+--------+------+
| timestamp | events | flag |
+-----------+--------+------+
|         1 | r      |    1 |
|         2 | r      |    0 |
|         3 | s      |    0 |
|         4 | r      |    0 |
|         5 | r      |    1 |
|         6 | r      |    1 |
|         7 | r      |    0 |
|         8 | s      |    0 |
|         9 | r      |    0 |
|        10 | r      |    0 |
|        11 | s      |    0 |
+-----------+--------+------+

到目前为止我尝试过的是

SELECT a.time, a.event, 0 as flag
FROM table1 AS a
JOIN table1 AS b
ON b.event = 's' AND abs(a.id - b.id) <= 1

我得到了我需要标记为0但错过了1的所有行

TimeStamp 是有序的时间，但为了便于解决，将其转换为 integer。

Answer 1

尝试以下操作：

With CTE As
(
  Select id, time, event,
  Case
      When event='r' then -10 else id
  End as f
  From table1
)
Select id, time, event,
Case 
    when id in 
    (select f from cte where f<>-1
    union all
    select f+1 from cte where f<>-1
    union all
    select f-1 from cte where f<>-1) then 0 else 1
End As flag
From CTE

When event='r' then -10 else id中的-10是id列中不存在的任何 integer 值，即使它已加 1。

查看db<>fiddle的演示。

Answer 2

另一种选择。 为了解决间隙的可能性，我使用 row_number 生成无间隙序列，然后使用自连接来避免 LEAD 和 LAG。

with cte as (select *, ROW_NUMBER() over (order by time) as rno from table1
)
select main.*, 
    case when main.event = 's' then 0 
    when main.event <> 's' and after.event = 's' then 0 
    when main.event <> 's' and prior.event = 's' then 0 
    else 1 end as [flag], 
    prior.rno as [r-1], prior.id as [prior id], prior.event as [prior event],
    after.rno as [r+1], after.id as [after id], after.event as [after event]
from cte as main 
left join cte as prior on main.rno = prior.rno + 1
left join cte as after on main.rno = after.rno - 1
order by main.rno;

小提琴演示 - 包含一些带有间隙的额外行来说明。 目前尚不清楚哪种逻辑最适合选择前/后行，因此我使用了“时间”列。