Ability to define LET/WITH statements on non-SELECT DML

Ability to Add WITH, LET statements for DML statements
At present only SELECT allows this. Allowing others might benefit

Evaluate rule out.
INSERT/UPSERT/MERGE – may not any use.
UPDATE (WITH may not useful unless JOIN is supported). That leaves with LET in UPDATE .

UPDATE default AS d

LET olddoc = d

SET ........

UNSET ....

WHERE ........

RETURNING olddoc, d;

https://forums.couchbase.com/t/access-old-values-from-returning-clause-of-update/26094/2