How to delete all value from a listing field in one category?

[Tim Copper]

Hi guys,

I'm trying to run a query to remove all value of listing field rental_price from category_id 2106 only
So I run this

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But I got error:

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I tried going to Structures in phpmyadmin to check on the Null checkbox and hit Save button, but it won't change.
Screen Shot 2022-03-15 at 3.44.11 PM.png

I did some research and found these code to change rental_price to nullable

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But none of them work

Is there any solution to this?
Thank you