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So your problem comes from the fact, that you have nested json string as a value.

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This is of course the case and I see this now. I think I might have been confused by not knowing enough by VARIANT and the fact that the online DBR SQL editor will do some helpful semi-transparent output formatting.

Thank you for your help - I can now do a lateral explode and recombine to original granularity. If not performant enough I will go upstream and see if something can be done closer to the source schema.