CODEWITHSUNDEEP
sqlsql-servert-sqlsql-server-2008null
Matt
Matt

Reputation: 4190

Return value from previous record if value is -1

I've got a table that contains a LocationId field. In some cases, where a record shares the same foreign key, the LocationId might come through as -1.

What I want to do is in my select query is in the case of this happening, the previous location.

Example data:

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

The -1 should come out as 456 for record 2, and 891 for record 4 and 5

Upvotes: 0

Views: 721

Answers (3)

ThomasMcLeod
ThomasMcLeod

Reputation: 7769

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

Upvotes: 1

srgerg
srgerg

Reputation: 19329

You can use a correlated subquery. For example:

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

Upvotes: 1

RichardTheKiwi
RichardTheKiwi

Reputation: 107736

For the entire result set

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

Upvotes: 2

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