Lynn Pettis (9/1/2014)
dwain.c (9/1/2014)
Not exactly a traditional gaps and islands problem but fun nevertheless. Here's a relatively simple alternative.
DECLARE @system_log TABLE(
PK_ID int PRIMARY KEY
,Sequence_ID int null
)
INSERT @system_log(
PK_ID
,Sequence_ID
)VALUES
(1035590, 35587),
(1035589, NULL),
(1035586, NULL),
(1035585, NULL),
(1035584, NULL),
(1035583, 35583),
(1035582, NULL),
(1035581, NULL),
(1035579, NULL),
(1035578, 35553),
(1035554, NULL),
(1035552, 35551),
(1035550, 35550)
SELECT PK_ID, Sequence_ID=CASE WHEN Sequence_ID IS NOT NULL THEN Sequence_ID ELSE
ROW_NUMBER() OVER (PARTITION BY rn2 ORDER BY PK_ID)-1 END
FROM
(
SELECT PK_ID, Sequence_ID
,rn2=MAX(Sequence_ID) OVER (ORDER BY PK_ID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM @system_log
) a
ORDER by PK_ID desc;
Dwain, I like yours as it appears to be more efficient than mine. I rewrote it slightly to make it cleaner in my opinion.
DECLARE @system_log TABLE(
PK_ID int PRIMARY KEY
,Sequence_ID int null
)
INSERT @system_log(
PK_ID
,Sequence_ID
)VALUES
(1035590, 35587),
(1035589, NULL),
(1035586, NULL),
(1035585, NULL),
(1035584, NULL),
(1035583, 35583),
(1035582, NULL),
(1035581, NULL),
(1035579, NULL),
(1035578, 35553),
(1035554, NULL),
(1035550, 35550);
WITH BaseData as (
SELECT
PK_ID,
Sequence_ID,
rn2 = MAX(Sequence_ID) OVER (ORDER BY PK_ID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
FROM
@system_log
)
SELECT
PK_ID,
Sequence_ID = CASE WHEN Sequence_ID IS NOT NULL
THEN Sequence_ID
ELSE ROW_NUMBER() OVER (PARTITION BY rn2 ORDER BY PK_ID) - 1
END
FROM
BaseData
ORDER BY
PK_ID DESC;
Thanks Lynn. Guess I skipped the last part of Make it Work, Make it Fast, Make it Pretty[/url]
🙂
My thought question: Have you ever been told that your query runs too fast?
My advice:
INDEXing a poor-performing query is like putting sugar on cat food. Yeah, it probably tastes better but are you sure you want to eat it?
The path of least resistance can be a slippery slope. Take care that fixing your fixes of fixes doesn't snowball and end up costing you more than fixing the root cause would have in the first place.
Need to UNPIVOT? Why not CROSS APPLY VALUES instead?[/url]
Since random numbers are too important to be left to chance, let's generate some![/url]
Learn to understand recursive CTEs by example.[/url]
[url url=http://www.sqlservercentral.com/articles/St