Unknown issue with Blending in Looker Studio

[jagathkumar-stf]

Hi all,
I’m facing an issue with a blended data source in Looker Studio. I created a chart using blending, but the numbers looked off. To debug, I made two separate charts:

1. Chart A [Jan 1 to Apr 5] – Uses the original BigQuery table directly.

   
   

2. Chart B [Jan 1 to Apr 5] – Uses a blended source, but includes only one data source (same as Chart A), with no joins.

   
   

Both charts use the same dimensions (date, phone_number) and the same metric (SUM(total_deposit)), but the results don’t match. Some records are missing in Chart B (from the blend), and the totals are lower.

This is how blending has been built (which is being used for chart B

This seems unusual because I’ve used blending before and never faced this issue. Could this be a bug or a known limitation in Looker Studio? @SZinsmeister @Indumathi @sam8

[阿泰]

I’m curious if you want to use the same resource (a chart), why not just use the BigQuery source instead of creating a new resource (blended source)? Blended data is meant for combining two or more data sources using a common key (dimension). If you’re only working with one source, I would recommend just using the BigQuery source directly.

[jagathkumar-stf]

Yes, I normally used blending with another table for join, but that version showed discrepancies in production dashboard.
So for debugging, I created a new blended data source using only the base table (no joins). Surprisingly, even this single-table blend gives incorrect results, as shown in my earlier message.