BigQuery Window ORDER BY is not allowed if DISTINCT is specified - window-functions

Question

I'm investigating porting some bigquery legacy sql containing windowed distinct counts like this
count(distinct brand_id) over (partition by user_id order by order_placed_at range between 7 * 24 * 60 * 60 * 1000000 PRECEDING AND 1 PRECEDING) as last_7_day_buyer_brands
to Standard sql.... but I get this error....
Window ORDER BY is not allowed if DISTINCT is specified
For reference I've tried APPROX_COUNT_DISTINCT function with no luck.
Is there a better way to get this to work other than write the subqueries and group by's?
Most of the other queries have ported to standard sql with only minor changes.

Answer 1

Per documentation
OVER clause requirements:
PARTITION BY: Optional.
ORDER BY: Optional. Disallowed if DISTINCT is present.
window_frame_clause: Optional. Disallowed if DISTINCT is present.
note: above is 'highlighted' by me, not as in documentation
As you can see not only ORDER BY but even RANGE BETWEEN is not allowed when DISTINCT is used
I think, subquery is the way to go.
In case if you need direction for this, use below simple example
#standardSQL
SELECT
user_id,
order_placed_at,
brand_id,
(SELECT COUNT(DISTINCT brand)
FROM UNNEST(last_7_day_buyer_brands_with_dups) AS brand
) AS last_7_day_buyer_brands
FROM (
SELECT
user_id,
order_placed_at,
brand_id,
ARRAY_AGG(brand_id) OVER(
PARTITION BY user_id ORDER BY order_placed_at
RANGE BETWEEN 7 * 24 * 60 * 60 * 1000000 PRECEDING AND 1 PRECEDING
) AS last_7_day_buyer_brands_with_dups
FROM yourTable
)