I need to look into this further, but its a very helpful piece of info (which I didn't realise), many thanks.

The code isn't as simple as the example I have posted, and instead of the NOT EXISTS I have shown there is quite a lot of

DOC.SomeAttribute IN

(

SELECT SomeID

FROM SomeTable

WERE SomeUserCredential = 'X'

...

and generally "= 'X' " also includes an OR with a further nested sub-select, often several levels deep, so, sadly, I think there is a racing-chance that the Optimiser decides on a SCAN somewhere along the way 🙁

I will keep that in mind from now on when I'm pouring over the Query Plans 🙂