Question

Fellow Query Writers,

I have a table as follows:

myTable t1
col2 col3
 2    1
 3    0
 4    0
 5    0
 6    0

and I want to update each zero on col3 with the value of col3 in the previous row plus the value of col2 in the current row. So my table would de like the following:

myTable t1
col2 col3
 2    1 
 3    4  (1+3)
 4    8  (4+4)
 5    13 (5+8) 
 6    19 (6+13)

I’m missing the logic here, short-sightedness perhaps. I was trying it with a cursor as follows:

DECLARE @var3 FLOAT

DECLARE cursor3 CURSOR FOR
SELECT col2, col3 FROM table1
FOR UPDATE OF col3
OPEN cursor3


FETCH FIRST FROM cursor3
WHILE (@@FETCH_STATUS > -1)
BEGIN
 UPDATE @table1
 SET col3 = isnull(@var3, 0) + isnull(col2, 0)
 WHERE CURRENT OF cursor3
 FETCH NEXT FROM cursor3 INTO @var3
END

but it’s wrong.
Any ideas?

Thanks in advance.

Answer 1

OK, Try this.

CREATE TABLE MyTable (Id INT Identity, Col2 int, Col3 int)

INSERT INTO MyTable (Col2, Col3)
VALUES (2,1), (3,0), (4,0),(5,0),(6,0)

SELECT * from MyTable

WHILE (SELECT COUNT(*) FROM MyTable WHERE Col3=0) > 0
BEGIN
    UPDATE TOP (1) MyTable
    SET CoL3 = (Mytable.col2 + (select col3 from mytable t2 where (t2.id = mytable.id-1)))
    WHERE Col3 = 0
END

SELECT * from MyTable

Uses a WHILE loop which should be faster than a cursor under most circumstances.