Recursive SQL query - using results from query within query - sql

Question

I'm running SQL Server 2012, and here's what I need:
Row Field1 Field2
1 0 1
2 ? 2
3 ? -5
I need a query that will go throw row by row.
It should take row2,field1 and set it equal to row1,field1+row2,field2
It then would take row3,field1 and set it equal to row2,field1+row3,field2
Initially the table has values in Field1 that are all equal to 0, and so when I run my query it just always uses 0 for the field1 values.
Any help would be appreciated. I was thinking a CTE would be the way to go, but I just don't know where to go with that.
Edit:
Just to clear up some things, in my example. The initial input would be
Row Field1 Field2
1 0 1
2 0 2
3 0 -5
The desired output would be:
Row Field1 Field2
1 1 1
2 3 2
3 -2 -5
My actual table is a bit complicated, but I know I can apply it specifically if I could understand how to pull it off with this example.

Answer 1

Is this what you need? (Unclear if when you refer to row2,field1 for example you mean the before or after update value)
CREATE TABLE YourTable
(
Row INT,
Field1 INT NULL,
Field2 INT
)
INSERT INTO YourTable
VALUES (1,0,1),
(2,0,2),
(3,0,-5);
WITH CTE AS
(
SELECT *,
SUM(Field2) OVER (ORDER BY Row ROWS UNBOUNDED PRECEDING) AS RunningTotal
FROM YourTable
)
UPDATE CTE
SET Field1 = RunningTotal
SELECT *
FROM YourTable
Final Result
Row Field1 Field2
----------- ----------- -----------
1 1 1
2 3 2
3 -2 -5
Or another (more literal) interpretation of your word problem might be
WITH CTE AS
(
SELECT *,
LAG(Field2) OVER (ORDER BY Row) AS PrevRowField2
FROM YourTable
)
UPDATE CTE
SET Field1 = PrevRowField2 + Field1
WHERE PrevRowField2 IS NOT NULL

Answer 2

Something like this adapted from TSQL A recursive update?
With cte As (
Select
Row,
Field1,
Field2
From
t
Where
Row = 1
Union All
Select
t.Row,
t.Field2 + c.Field1,
t.Field2
From
t
Inner Join
cte c
On t.Row = c.Row + 1
)
Update
t
Set
Field1 = c.Field1
From
t
inner join
cte c
On t.Row = c.Row
http://sqlfiddle.com/#!6/cf843/1