SQL: How to fill empty cells with previous row value?

Question

I need to produce the column \"required\" in the following table using SQL without using loops and correlated sub queries. Is this possible in SQL 2008?

Date         


        

Answer 1

How about a left outer join on the same table where the date is less than the current one and the value is non-empty, ordered by date desc (limit 1), returning zero when null ? (No server available to test at the moment). Unless this counts as a sub-query...