Question

Table has 2 cols: [nr] and [diff]

diff is empty (so far – need to fill)

nr has numbers:

 1
 2
 45
 677
 43523452

on the diff column i need to add the differences between pairs

 1 | 0
 2 | 1
 45 | 43
 677 | 632
 43523452 | 43522775

so basically something like :

 update tbl set diff = @nr - @nrold where nr = @nr

but i don’t want to use fetch next, because it’s not cool, and it’s slow (100.000) records

how can I do that with one update?

Answer 1

CREATE TABLE #T(nr INT,diff INT)

INSERT INTO #T (nr) SELECT 1 
              UNION SELECT 2 
              UNION SELECT 45 
              UNION SELECT 677 
              UNION SELECT 43523452

;WITH cte AS
(
SELECT nr,diff, ROW_NUMBER() OVER (ORDER BY nr) RN
FROM #T
)
UPDATE c1
SET diff = ISNULL(c1.nr - c2.nr,0)
FROM cte c1
LEFT OUTER JOIN cte c2 ON c2.RN+1= c1.RN

SELECT nr,diff FROM #T

DROP TABLE #T