Find First and Last Period without holes

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Find First and Last Period without holes

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Umfriend

Posted Monday, January 14, 2013 6:02 AM

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OK, first post and Subject I can not phrase any better.

1. I have a table where all records have a field for period.
2. For each record I want to know what the first and last periods are in which the period of the current record falls, without missing periods.

Assume Table t1:
KEY Period Data (Key is three fields + Period)
A 5 data
A 6 data
A 8 data

I want a query that yields:
KEY Period Data FirstPeriod LastPeriod
A 5 data 5 6
A 6 data 5 6
A 8 data 8 8

I have got it but it must be extremely inefficient. I do (for FP (FirstPeriod) only, LP is similar):
UPDATE t1
SET FP = (
SELECT MAX(Period)
FROM
( SELECT t2.KEY, t2.Period
FROM vAT t2
LEFT JOIN vAT t3
ON t2.KEY = t3.KEY
AND t2.Per = t3.Per+1
WHERE t3.Per IS NULL
AND t1.KEY = t2.KEY AND t1.Per >= t2.Per
) as tfp
)

FROM vAT t1

It does what I need but this can't be right/efficient, can it?

Kind rgds,
Umf

Post #1406679

Umfriend

Posted Monday, January 14, 2013 8:10 AM

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Last Login: Monday, February 18, 2013 1:37 AM
Points: 2, Visits: 11

Oh well. I have many many rows with but (relatively) few distinct occurences of KEY (without Period). Using temporary tables solved the performance thing (5 mins to 12 secs). May integrate in some subquery structure again but for now I am fine.

Many thanks.

Post #1406752

dwain.c

Posted Tuesday, January 15, 2013 7:30 PM

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Last Login: Yesterday @ 6:03 AM
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I understand you already have a solution but this might be a bit more efficient. The technique is based on an article by Jeff Moden on Grouping Islands of Contiguous Dates (your periods are like dates).

DECLARE @Test TABLE
    ([KEY] VARCHAR(5), Period INT, Data VARCHAR(10))

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',8,'data'

;WITH CTE AS (
    SELECT [Key], FirstPeriod=MIN(Period), LastPeriod=MAX(Period)
    FROM (
        SELECT [KEY], Period, Data
            ,n=Period-ROW_NUMBER() OVER (PARTITION BY [KEY] ORDER BY Period)
        FROM @Test) a
    GROUP BY [Key], n)
SELECT b.[KEY], Period, Data, FirstPeriod, LastPeriod
FROM CTE a
INNER JOIN @Test b ON a.[KEY] = b.[KEY] AND b.Period BETWEEN FirstPeriod AND LastPeriod

Hope this helps!

No loops! No CURSORs! No RBAR! Hoo-uh!

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?

Need to UNPIVOT? Why not CROSS APPLY VALUES instead?
Since random numbers are too important to be left to chance, let's generate some!
Are you too recursively challenged?
Splitting strings based on patterns can be fast!

Post #1407546

Bhanu Prakash T

Posted Thursday, January 17, 2013 3:56 AM

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Last Login: Monday, January 28, 2013 12:49 AM
Points: 107, Visits: 36

You can check this as well. Slightly improved version. Is n't it ?

DECLARE @Test TABLE
([KEY] VARCHAR(5), Period INT, Data VARCHAR(10))

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',8,'data'

;WITH CTE AS (
SELECT [Key], Period, Data, FirstPeriod=MIN(Period) OVER (partition by [key], n), LastPeriod=MAX(Period) OVER (partition by [key], n)
FROM (
SELECT [KEY], Period, Data, n=Period-ROW_NUMBER() OVER (PARTITION BY [KEY] ORDER BY Period)
FROM @Test) a
)
SELECT [Key], Period, Data, FirstPeriod, LastPeriod
FROM CTE a;

Thank you.

Post #1408304

Sergiy

Posted Wednesday, February 13, 2013 7:06 PM

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Group: General Forum Members
Last Login: Today @ 8:36 AM
Points: 4,557, Visits: 8,212

dwain.c (1/15/2013)

DECLARE @Test TABLE
    ([KEY] VARCHAR(5), Period INT, Data VARCHAR(10))

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',8,'data'

;WITH CTE AS (
    SELECT [Key], FirstPeriod=MIN(Period), LastPeriod=MAX(Period)
    FROM (
        SELECT [KEY], Period, Data
            ,n=Period-ROW_NUMBER() OVER (PARTITION BY [KEY] ORDER BY Period)
        FROM @Test) a
    GROUP BY [Key], n)
SELECT b.[KEY], Period, Data, FirstPeriod, LastPeriod
FROM CTE a
INNER JOIN @Test b ON a.[KEY] = b.[KEY] AND b.Period BETWEEN FirstPeriod AND LastPeriod

Hope this helps!

The script goes nuts if you add another record to the table;

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',6,'other data'
UNION ALL SELECT 'A',8,'data'

Post #1419795

dwain.c

Posted Wednesday, February 13, 2013 7:14 PM

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Group: General Forum Members
Last Login: Yesterday @ 6:03 AM
Points: 2,345, Visits: 3,191

Sergiy (2/13/2013)

dwain.c (1/15/2013)

DECLARE @Test TABLE
    ([KEY] VARCHAR(5), Period INT, Data VARCHAR(10))

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',8,'data'

;WITH CTE AS (
    SELECT [Key], FirstPeriod=MIN(Period), LastPeriod=MAX(Period)
    FROM (
        SELECT [KEY], Period, Data
            ,n=Period-ROW_NUMBER() OVER (PARTITION BY [KEY] ORDER BY Period)
        FROM @Test) a
    GROUP BY [Key], n)
SELECT b.[KEY], Period, Data, FirstPeriod, LastPeriod
FROM CTE a
INNER JOIN @Test b ON a.[KEY] = b.[KEY] AND b.Period BETWEEN FirstPeriod AND LastPeriod

Hope this helps!

The script goes nuts if you add another record to the table;

INSERT INTO @Test
SELECT 'A',5,'data'
UNION ALL SELECT 'A',6,'data'
UNION ALL SELECT 'A',6,'other data'
UNION ALL SELECT 'A',8,'data'

I guess that would depend on whether the OPs data contains duplicates on KEY. In which case I'd agree that this approach won't work.

Post #1419797

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