Update based on previous value SQL SERVER 2005

Question

I need to Update these NULL Values:

PK |  CODE
---+-------
1  |   20
2  |   NULL
3  |   NULL
4  |   30
5  |   NULL
6  |   NULL
7  |   NULL
8  |   40
9  |   NULL

Like this:

PK   |   CODE
-----+------------
1    |    20
2    |    20
3    |    20
4    |    30
5    |    30
6    |    30
7    |    30
8    |    40
9    |    40

It should always be based on the last minimum value.

I have tried the code below, but it just updates the first row before the one who had value at the beginning.

QUERY

UPDATE TT 
SET CODE = (SELECT CODE 
FROM #TSPV_TEMP T2 with(nolock)
WHERE T2.KEY = (tt.KEY -1))
FROM #TSPV_TEMP TT with (nolock)
WHERE tt.CODE IS NULL

Answer 1

You can do this as:

UPDATE TT 
    SET CODE = (SELECT TOP 1 CODE
                FROM #TSPV_TEMP T2 with(nolock)
                WHERE T2.KEY < tt.KEY AND
                      CODE IS NOT NULL
                ORDER BY KEY DESC
               )
    FROM #TSPV_TEMP TT with (nolock)
    where tt.CODE IS NULL;

Note the differences in the subquery. This looks for the previous non-NULL value for CODE for the update.