asked on

SQL query to compare the previous row and current values

I need some help.
I need to compare the value of previous row with the value of current row in a table in SQL Server 2008.
Table name is tbHeight with four (4) colunms.
measurements of height is done once a month. the height of current month should be higher than the height from previous month.
if value of current month (row) is lower than value of previous month then flag and listed in the output.
see attached for sample data and output.
thanks in advance.

output
-----------------------------------------------
pid      MDATE      MHEIGHT
1      7-Aug-10      60
4      23-May-10      55.9
5      24-Mar-10      56.7
TBHEIGHT1.xlsx

deighton

for a table called AHEIGHT (in my example, please change to your table name)

select B.*FROM aheight B where B.MHeight < (SELECT TOP 1 A.MHeight FROM aHEIGHT A
WHERE A.MDATE < B.MDATE ORDER BY A.MDATE DESC) AND EXISTS(SELECT NULL FROM aHEIGHT C WHERE B.MDATE < C.MDATE)

deighton

formatting vanished there, here is repost, code the same though

select B.* FROM aheight B 
                where B.MHeight < 
                     (SELECT TOP 1 A.MHeight FROM aHEIGHT A 
	                                                       WHERE 
                                                                           A.MDATE < B.MDATE ORDER BY A.MDATE DESC)
                                                               AND EXISTS(SELECT NULL FROM aHEIGHT C 
                                                                           WHERE B.MDATE < C.MDATE)

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Rajkumar Gs

Try this query. #Table is table name that I give. Correct it your actual table name.

WITH CTE AS
(
SELECT *, ROW_NUMBER() OVER(ORDER BY pid, MDATE ) Serial FROM #table
)
SELECT a.* FROM CTE a
	LEFT JOIN CTE b ON a.Serial - 1 = b.Serial AND a.pid = b.pid
	WHERE b.MHEIGHT > a.MHEIGHT

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This is how I tested it

CREATE TABLE #table
(
	pid      INT,
	MDATE    DATETIME,
	MHEIGHT	 DECIMAL(18,2)
)

INSERT INTO #table
SELECT 1,	'10-Mar-10',	49.2 UNION ALL
SELECT 1,	'11-Apr-10',	52 UNION ALL
SELECT 1,	'9-May-10',	55 UNION ALL
SELECT 1,	'13-Jul-10',	62.5 UNION ALL
SELECT 1,	'7-Aug-10',	60 UNION ALL
SELECT 1,	'8-Sep-10',	62.9 UNION ALL
SELECT 1,	'7-Oct-10',	63.5 UNION ALL
SELECT 2,	'14-Mar-10',	53.1 UNION ALL
SELECT 2,	'11-Apr-10',	55.2 UNION ALL
SELECT 2,	'29-May-10',	61.3 UNION ALL
SELECT 2,	'12-Jun-10',	62.1 UNION ALL
SELECT 2,	'13-Jul-10',	63.4 UNION ALL
SELECT 2,	'15-Aug-10',	63.6 UNION ALL
SELECT 2,	'30-Sep-10',	65.5 UNION ALL
SELECT 2,	'16-Oct-10',	66.9 UNION ALL
SELECT 3,	'14-Mar-10',	57.3 UNION ALL
SELECT 3,	'18-Apr-10',	57.6 UNION ALL
SELECT 3,	'13-May-10',	60.3 UNION ALL
SELECT 3,	'14-Jul-10',	64.5 UNION ALL
SELECT 3,	'16-Aug-10',	65.3 UNION ALL
SELECT 3,	'14-Sep-10',	65.4 UNION ALL
SELECT 4,	'22-Mar-10',	53.7 UNION ALL
SELECT 4,	'21-Apr-10',	57.5 UNION ALL
SELECT 4,	'23-May-10',	55.9 UNION ALL
SELECT 4,	'20-Jun-10',	58.7 UNION ALL
SELECT 4,	'20-Jul-10',	62.8 UNION ALL
SELECT 4,	'19-Aug-10',	63.7 UNION ALL
SELECT 4,	'20-Sep-10',	66.2 UNION ALL
SELECT 4,	'21-Oct-10',	67.2 UNION ALL
SELECT 5,	'21-Apr-10',	69.2 UNION ALL
SELECT 5,	'19-May-10',	58.6 UNION ALL
SELECT 5,	'24-Mar-10',	56.7


-- main query
WITH CTE AS
(
SELECT *, ROW_NUMBER() OVER(ORDER BY pid, MDATE ) Serial FROM #table
)
SELECT a.* FROM CTE a
	LEFT JOIN CTE b ON a.Serial - 1 = b.Serial AND a.pid = b.pid
	WHERE b.MHEIGHT > a.MHEIGHT
	
DROP TABLE #table

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Rajkumar Gs

Or it could be

WITH CTE AS
(
SELECT *, ROW_NUMBER() OVER(ORDER BY pid, MDATE ) Serial FROM #table
)
SELECT x.*, CASE WHEN y.pid IS NOT NULL THEN 'FLAG' ELSE NULL END FLAG FROM CTE x
LEFT JOIN
(
SELECT a.*
FROM CTE a
	LEFT JOIN CTE b ON a.Serial - 1 = b.Serial AND a.pid = b.pid
	WHERE b.MHEIGHT > a.MHEIGHT
) y ON x.pid = y.pid AND x.MDATE = y.MDATE

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Replacing #table with your tablename

Rajkumar Gs

Corrected

WITH CTE AS
(
SELECT *, ROW_NUMBER() OVER(ORDER BY pid, MDATE ) Serial FROM #table
)
SELECT x.*, CASE WHEN y.pid IS NOT NULL THEN 'FLAG' ELSE '' END FLAG FROM CTE x
LEFT JOIN
(
SELECT a.*
FROM CTE a
	LEFT JOIN CTE b ON a.Serial - 1 = b.Serial AND a.pid = b.pid
	WHERE b.MHEIGHT > a.MHEIGHT
) y ON x.pid = y.pid AND x.MDATE = y.MDATE

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Change #table to your tablename

Raj

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Rajkumar Gs

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LougaLo

ASKER

deighton:
i ran your query here is the output i got. i need to show (flag) only higher curent values. thanks

PId      mdate      mheight
1      2010-05-09      55
1      2010-08-07      60
1      2010-09-08      62.9
1      2010-10-07      63.5
1      2010-04-11      52
2      2010-04-11      55.2
2      2010-09-30      65.5
4      2010-04-21      57.5
4      2010-05-23      55.9
4      2010-06-20      58.7
4      2010-07-20      62.8
4      2010-08-19      63.7
5      2010-05-19      58.6

LougaLo

ASKER

RajkumarGS:
thank you it works fine.

deighton

in that case, maybe

select B.* FROM aheight B 
                where B.MHeight < 
                     (SELECT TOP 1 A.MHeight FROM aHEIGHT A 
	                                                       WHERE 
                                                                          A.pid = b.pid and  A.MDATE < B.MDATE ORDER BY A.MDATE DESC)
                                                               AND EXISTS(SELECT NULL FROM aHEIGHT C 
                                                                           WHERE b.pid = c.pid and B.MDATE < C.MDATE)

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