如果值为 -1，则返回上一条记录的值

Question

我有一个包含 LocationId 字段的表。在某些情况下，如果记录共享相同的外键，则 LocationId 可能会显示为 -1。

我想要做的是在发生这种情况的情况下，在我的选择查询中查找之前的位置。

示例数据：

Record  FK     StartTime               EndTime          Location
1       110  2011/01/01 12.30        2011/01/01 6.10      456
2       110  2011/01/01 3.40         2011/01/01 4.00       -1
3       110  2011/01/02 1.00         2011/01/02 8.00      891
4       110  2011/01/02 5.00         2011/01/02 6.00       -1
5       110  2011/01/02 6.10         2011/01/02 6.30       -1

记录 2 的 -1 应为 456，记录 4 和 5 的 -1 应为 891

Answer 1

对于整个结果集

with tmp(Record ,FK ,StartTime ,EndTime ,Location)
as( select
1, 110 ,'2011/01/01 12:30', '2011/01/01 6:10', 456 union all select
2, 110 ,'2011/01/01 3:40', '2011/01/01 4:00', -1 union all select
3, 110 ,'2011/01/02 1:00', '2011/01/02 8:00', 891 union all select
4, 110 ,'2011/01/02 5:00', '2011/01/02 6:00', -1 union all select
5, 110 ,'2011/01/02 6:10', '2011/01/02 6:30', -1
)

-- ignore above this line
select curr.Record, curr.FK, curr.StartTime, curr.EndTime,
 case when curr.Location=-1 then prev.Location else curr.Location end Location
from tmp curr
outer apply 
 (select top 1 prev.location
 from tmp prev
 where curr.location=-1 and prev.FK=curr.FK
 and prev.starttime < curr.starttime
 and prev.location <> -1
 order by prev.starttime desc) prev

Answer 2

您可以使用相关子查询。例如：

SELECT *
    , (SELECT TOP 1 Location
       FROM MyTable T2
       WHERE T2.Record <= T1.Record
       AND T2.FK = T1.FK
       AND T2.Location <> -1
       ORDER BY T2.Record DESC) AS BestLocation
FROM MyTable T1

Answer 3

SELECT
    Record,
    FK,
    StartTime,
    EndTime,
(
    SELECT
        Location
    FROM
        MyTable
    WHERE
        Record =
    ( 
        SELECT
            MAX(Record)
        FROM
            MyTable t2
        WHERE
            t2.Record =< t1.Record AND
            Location >= 0
    )
) 

FROM
    MyTable t1