# Transform - Fill missing time series points

**URL:** <https://community.grafana.com/t/transform-fill-missing-time-series-points/152825>\
**Category:** Grafana\
**Tags:** time-series, transformations, grafana\
**Created:** [June 17, 2025, 2:10pm UTC](https://community.grafana.com/t/transform-fill-missing-time-series-points/152825 "2025-06-17T14:10:25Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![oli](https://avatars.discourse-cdn.com/v4/letter/o/2bfe46/32.png) [@oli](https://community.grafana.com/u/oli)\
**Post date:** [June 17, 2025, 2:10pm UTC](https://community.grafana.com/t/transform-fill-missing-time-series-points/152825/1 "2025-06-17T14:10:25Z")

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Hi All,  
I have data coming from a narrow Timestream database, the timestamps for the different series are not synchronised - as they are only sent when the data has changed more than a set amount.

I need to sum two of the series “Series A” and “Series B”.  
To do this I have been trying to use the “Add field from calculation” → “Reduce Row” → “Last \*” function as I believed this would fill in the null values with the last reading.  
However it doesn’t seem to do anything to my data.

Does anyone know what I have missed?

 ![image](https://us1.discourse-cdn.com/grafana/original/3X/7/5/759b3d4566d765ee8b748b9e1ebf705bdb2ea835.png)

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**Author:** ![dawiddebowski](https://sea2.discourse-cdn.com/grafana/user_avatar/community.grafana.com/dawiddebowski/32/49435_2.png) [@dawiddebowski](https://community.grafana.com/u/dawiddebowski)\
**Post date:** [June 17, 2025, 7:56pm UTC](https://community.grafana.com/t/transform-fill-missing-time-series-points/152825/2 "2025-06-17T19:56:43Z")

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Hi, AFAIK Add field from calculation will take default 0 if the field is empty (you can see that in your Total column), so if your case is just sum A and B in each timestamp - it’s just it.  
UNLESS what you want is to have two numbers as a result - sum of all values of series A and sum of all values of series B (which I’ve thought about just now), you can then use Reduce transformation (something like that) that will reduce each column with a certain calculation (use total for your case).

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**Author:** ![oli](https://avatars.discourse-cdn.com/v4/letter/o/2bfe46/32.png) [@oli](https://community.grafana.com/u/oli)\
**Post date:** [June 24, 2025, 7:17am UTC](https://community.grafana.com/t/transform-fill-missing-time-series-points/152825/3 "2025-06-24T07:17:23Z")

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Sorry for the slow reply, that seems to match what I have found. The closest effect I have found so far is (mis)using a centred mean with a small window, however this will only fill in short gaps.  
Is there any way to fill downwards using the last value in a transformation or another way to calculate the sum using the last value of each column?

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**Author:** ![grant2](https://sea2.discourse-cdn.com/grafana/user_avatar/community.grafana.com/grant2/32/42281_2.png) [@grant2](https://community.grafana.com/u/grant2)\
**Post date:** [June 24, 2025, 9:48am UTC](https://community.grafana.com/t/transform-fill-missing-time-series-points/152825/4 "2025-06-24T09:48:57Z")

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> [@oli](#):
>
> Is there any way to fill downwards using the last value in a transformation or another way to calculate the sum using the last value of each column?

Maybe try using the new (still in private preview) Transform by SQL Expressions?

> **[SQL expressions | Grafana documentation](https://grafana.com/docs/grafana/latest/panels-visualizations/query-transform-data/sql-expressions/)**
>
> Manipulate and transform data in Grafana using SQL expressions.