how to update multiple values null using multiple case statements

Question

This is my table:

Site_name | date& Time              | PowerOutput         
----------+-------------------------+------------------
ACT0001   | 2013-07-21 01:00:00.000 | 196.852984494331   
ACT0001   | 2013-07-21 02:00:00.000 |   0   
xyz0001   | 2013-07-21 03:00:00.000 | 196.852984494331   
xyq0001   | 2013-07-21 04:00:00.000 | 196.958395639561 
xys0001   | 2013-07-21 05:00:00.000 |   0
xyd0001   | 2013-07-21 06:00:00.000 | 197.20098185022 
xye0001   | 2013-07-21 07:00:00.000 |   0 
xyg0001   | 2013-07-21 08:00:00.000 |   0     
cfg0001   | 2013-07-21 09:00:00.000 | 197.412144323522 
acb0001   | 2013-07-21 10:00:00.000 |   0 
bdf0001   | 2013-07-21 11:00:00.000 |   0 
olk0001   | 2013-07-21 12:00:00.000 | 196.886233049016 

I have this table and I am trying to update the values in places of "ZERO's". If there is only one zero then I am able to update the table, but if there are consecutive zero's I am finding it difficult to update the table.

The logic is :

• ((Previous value-next value)/previous value)*100 <5

  If this is true then it should insert the previous value

• ((Previous value-next value)/previous value)*100 >=5

  If this is true then it should remain as zero.

This is the code I have so far:

with cte as
(
    SELECT  
        *,
        lead(pr_output,1) OVER (ORDER BY (select null)) As PreviousValue,
        lag(pr_output,1) OVER (ORDER BY (select null)) As NextValue
    FROM
        [dbo].[Mytable]
)
,ctee as
(
    select 
        *,
        abs((PreviousValue*100-NextValue*100)/NextValue) as CheckFlag
    from
        cte 
)
select
    Site_name,[DATE&Time],
    case 
        when pr_output <>0 then pr_output
        else
            case 
                when CheckFlag >= 5 then 0
                else PreviousValue
            end
    end as pr_output
from 
    ctee

The error I am getting is

Divide by zero error encountered.

Please tell me what am I doing wrong. If their is an alternate way of doing this through?

Any help is appreciated.

output should be:

Site_name | date& Time              | PowerOutput         
----------+-------------------------+------------------
ACT0001   | 2013-07-21 01:00:00.000 | 196.852984494331   
ACT0001   | 2013-07-21 02:00:00.000 | 196.852984494331   
xyz0001   | 2013-07-21 03:00:00.000 | 196.852984494331   
xyq0001   | 2013-07-21 04:00:00.000 | 196.958395639561 
xys0001   | 2013-07-21 05:00:00.000 | 196.958395639561
xyd0001   | 2013-07-21 06:00:00.000 | 197.20098185022 
xye0001   | 2013-07-21 07:00:00.000 |   0 
xyg0001   | 2013-07-21 08:00:00.000 |   0     
cfg0001   | 2013-07-21 09:00:00.000 | 197.412144323522 
acb0001   | 2013-07-21 10:00:00.000 |   0
bdf0001   | 2013-07-21 11:00:00.000 |   0 
olk0001   | 2013-07-21 12:00:00.000 | 196.886233049016 

Answer 1

Need to check if NextValue is zero before dividing by it..

Hope this solves your problem.

with cte as
(
    SELECT  
        *,
        lead(pr_output,1) OVER (ORDER BY (select null)) As PreviousValue,
        lag(pr_output,1) OVER (ORDER BY (select null)) As NextValue
    FROM
        [dbo].[Mytable]
)
,ctee as
(
    select 
        *,
        abs((PreviousValue*100-NextValue*100)/(case when NextValue = 0 then 1 else NextValue end)) as CheckFlag
    from
        cte 
)
select
    Site_name,[DATE&Time],
    case 
        when pr_output <>0 then pr_output
        else
            case 
                when CheckFlag >= 5 then 0
                else PreviousValue
            end
    end as pr_output
from 
    ctee