Multiple increments for sequences used in VALUES clauses.

Currently evaluation of the key, value and option elements of a VALUES clause are performed independently so sequence generation is not correctly shared.  Furthermore, within any element, sequence generation is not cached.  This means every execution of NEXTVAL generates a new value when it really should be generating a single value per VALUES clause.

e.g.

cbq> INSERT INTO default

   2 VALUES(to_string(NEXTVAL FOR default.s1.q1),{"a":NEXTVAL FOR default.s1.q1,"b":NEXTVAL FOR default.s1.q1});

...

cbq> SELECT meta().id, * FROM default;

...

    "results": [

    {

        "id": "0",

        "default": {

            "a": 2,

            "b": 1

        }

    }

    ],

• All are new values
• Within the "value", "b" may be generated before "a" (not strictly predictable since the elements are generated via map iteration)

We do indicate this here: https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/sequenceops.html#examples  (example 3)

You can workaround this using PREVVAL after the "key" has been generated, i.e.

INSERT INTO default

VALUES(to_string(NEXTVAL FOR default.s1.q1),{"a":PREVVAL FOR default.s1.q1,"b":PREVVAL FOR default.s1.q1});

but this won't work well for a contented sequence (as all refer to the global value, rather than a document/clause specific value).

For standards compliance I believe we should be generating a single value per sequence per VALUES clause.