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Trouble Joining Google Ads Tables in Looker Studio Using Helper Table – "Invalid Argument Type" Err

Posted on 05-13-2025 08:06 AM
rayray456
Bronze 1
Bronze 1
Reply posted on --/--/---- --:-- AM

Hi all,

I’m having trouble blending three tables in Looker Studio (formerly Google Data Studio) using a helper months table as the join key. I keep running into an “Invalid argument type” error and can’t get the join to work as expected.

My setup:

  • Helper Months Table: Contains a single column with all months in my reporting range (e.g., 2023-01, 2023-02, etc.), formatted as Month Year.Screenshot 2025-05-13 at 11.02.38 AM.pngScreenshot 2025-05-13 at 10.57.09 AM.png

  • Table A: Google Ads table with "Month" selected as the date dimension, but only includes months where there is data.

  • Table B: Another Google Ads table with "Month" selected, also only includes months where there is data.

  • I want to blend these so I get a complete list of months, with nulls where Table A or B have no data for a given month.

What I’ve tried:

  • Made the Helper Months table the leftmost table in the blend.

  • Attempted to join Table A and Table B to Helper Months using a full outer joinsScreenshot 2025-05-13 at 11.00.26 AM.png

  • Helper Months were Month Year.

  • Refreshed fields and rebuilt the blend multiple times.

The problem:

  • I keep getting an “Invalid argument type” error when I try to use the blend in a chart or table.

Questions:

  1. Is there a best practice for joining tables like this when not all tables have every month in the range?

  2. Any troubleshooting tips for resolving the “Invalid argument type” error in this context?

 Screenshots of the two individual table/data I"m trying to join to one.

Screenshot 2025-05-13 at 10.58.32 AM.png

 

Screenshot 2025-05-13 at 10.59.29 AM.png

 

 

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Posted on --/--/---- --:-- AM
sam8
Staff
Reply posted on --/--/---- --:-- AM

I think you're close! 

It should be totally fine to join tables even if not all the tables have values for all of the join key. That's when you want to think about whether you want an inner join, left join, full join, etc. But none of that would contribute to an error.

This error is about mismatched data types - for example if you try and join a string to a number. My guess is that not all of your month dimensions match that "year month" data format from your second screenshot. They might just be regular month dimensions. It might help to create a calculated field that converts your dates to a year month format, like "FORMAT_DATE(your_date_field, '%b %Y')"

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