Why would set not work?
https://cookbook.nodered.org/basic/move-message-property
The Set also works. And there is no way to tell before each actual use case which one is correct.
Using Move avoids unnecessary duplicates of data. And it is given to user in one step. Comes handy if project grows as you can imagine.
But I think the cookbook page or Change node info can be improved to help users understand benefit of correct usage of those commands.
Iām sure a pull request would be welcome
With my English? No way 
Let's keep the topic clear for UI Dropdown issue.
Meanwhile... the actual error would seem to be the extra . in the property
You need it as per @colin ' s post above msg.payload[0]["COUNT( DISTINCT uuid)"]
if you use the [ ] syntax you don't use . as well.
gotcha! Thank you
