If value is null get the one from before-CodePudding

How to get last row's value if current value is null?

I tried using LAG, but it returns null after second row.

SELECT timestamp, min, lag(min) over (order by id asc) as lag
from table

CodePudding user response：

From your description, you can try to SUM window function make a group then use max/min window function.

SELECT `timestamp`, 
     `min`,
      CASE WHEN `min` IS NULL THEN MAX(`min`) OVER(PARTITION BY grp order by id asc)  END
FROM (
    SELECT `timestamp`, 
           `min`, 
           SUM(CASE WHEN `min` IS NOT NULL THEN 1 ELSE 0 END) OVER(order by id asc) grp
    from `table`
) t1

sqlfiddle