Simply use:

;with cte as (SELECT id,Date,sno,bin,batch,DATEDIFF(second,LAG(Date,1) OVER(ORDER BY Date),Date) AS interval
   FROM bin1_final)

update cte set gap_int = interval

I assume that Id is the primary key (unique) in your table.

>Dear Sir,
>
>I have these codes
>
>

>  SELECT id,Date,sno,bin,batch,DATEDIFF(second,LAG(Date,1) OVER(ORDER BY Date),Date) AS alias
>   FROM bin1_final
>

>
>the above codes work fine, no issue.
>
>Now I want to update column with above codes like this
>
>

> update bin1_final set gap_int=(
>     SELECT DATEDIFF(second,LAG(Date,1) OVER(ORDER BY Date),Date) as ddif
>   FROM bin1_final)
>

>
>But it says:
>
>Msg 512, Level 16, State 1, Line 1
>Subquery returned more than 1 value. This is not permitted when the subquery follows ............ or' when the subquery is used as an expression.
>The statement has been terminated.
>
>Please help