Question

I need some advice.

I have a column with nulls in a field at a particular time period.

Name     Date
-----    -----
Cat      1/1/2012
Dog      1/2/2012
Fish     1/3/2012
NULL     1/4/2012
Goat     1/5/2012
NULL     1/6/2012
Sheep    1/7/2012

In the example above, how would I write a SQL statement to select the last known value for column Name whenever there is a null value in the column?

For instance I’d like the table to look like this:

Name      Date
-----    -----
Cat        1/1/2012
Dog        1/2/2012
Fish       1/3/2012
Fish       1/4/2012
Goat       1/5/2012
Goat       1/6/2012
Sheep      1/7/2012

---

Would this pseudo-code work?

Select 
isnull(Name, "Select Name from Table where Date = GetDate() - 1")
,Date
From Table

Answer 1

Try this [v is original, v2 is calculated new value] :

DECLARE @table table(v varchar(10), d varchar(10))
INSERT INTO @table 
SELECT 'Cat','1/1/2012' UNION
SELECT 'Dog','1/2/2012' UNION
SELECT 'Fish','1/3/2012' UNION
SELECT NULL,'1/4/2012' UNION
SELECT 'Goat','1/5/2012' UNION
SELECT NULL,'1/6/2012' UNION
SELECT 'Sheep','1/7/2012'


SELECT A.v, A.d, ISNULL(A.v,B.v) V2
FROM @table A
OUTER APPLY (   SELECT TOP 1 *
                FROM @table 
                WHERE d < A.d
                AND v IS NOT NULL
                ORDER BY d desc) B
order by d