Resolving Data Blending and Filtering Issues in Looker Studio
If you’ve ever tried blending data from multiple Google Analytics 4 (GA4) properties in Looker Studio, you might have run into some serious headaches. Data totals not adding up? Filters refusing to work? You’re not alone. This is an ongoing bug in Looker Studio, and frustratingly, no official fix has been released yet.
I recently faced this exact issue while working with a platform that, due to historical reasons, had two separate GA4 properties. An existing Looker Studio report had been built using only one of these properties, but a new request required consolidating data from both. What seemed like a straightforward task quickly turned into a nightmare — incorrect totals, broken filters, and no clear solution in sight.
After days of troubleshooting, I finally discovered a workaround that actually works. If you’re struggling with the same problem, here’s how you can fix it yourself.
Issue #1: Incorrect Data Blending
When combining data from multiple GA4 properties, Looker Studio often miscalculates the totals. For example, I was trying to merge the article view counts from two GA4 properties for a particular page path over a set date range — but the blended report gave me completely wrong numbers.
Solution #1: Fixing Data Aggregation with COALESCE
To make sure the total view count was accurate, I used the COALESCE function to merge page path and screen class fields from both GA4 tables:
COALESCE (Page path and screen class (Table 1), Page path and screen class (Table 2))This trick combined the data correctly, fixing the incorrect totals.
Issue #2: Filters That Do Nothing
The filters on blended data simply refused to work. The dimension I was trying to filter with was page path and screen class, but Looker Studio wouldn’t recognize it properly in the blended data. No matter how I set them up, selecting a specific page path had zero effect on the charts.
Solution #2: Making Filters Work with Field ID Manipulation
This required a more complex and unconventional approach. Filters weren’t working because Looker Studio struggled to recognize the blended fields (the bug, remember?). Here’s how I fixed it:
1. Duplicate the Filter Fields: Because I planned to filter the reports using the page path and screen class field, I created a new field named page path and screen class 0 in each of the GA4 tables and duplicated the original fields.
Note: When creating a new field, you can also customize the Field ID (this will come in handy).
2. Add These to the Blend: I included these new fields as Dimensions in the blend.
3. Update the Filter Control Field: I edited the control field in the filter to use these new fields. Used the COALESCE function again:
COALESCE (page path and screen class 0 (Table 1), page path and screen class 0 (Table 2))
4. Find the Field IDs: Temporarily hiding page path and screen class 0 broke the charts, revealing the required Field ID in the formula tab.
5. Assign Field IDs: I created 2 new page path and screen class fields each in both tables (page path and screen class 1 and page path and screen class 2) and manually assigned the Field IDs to match those found in step 4.
6. Reactivate Everything: Restored page path and screen class 0. Saved, refreshed and — boom! — filters finally worked.
THE END
Hopefully, Google will address these issues soon, but until then, this method should help you navigate the challenges of data blending and filters in Looker Studio.
