Using Parameter within timestamp_trunc in SQL Query for DataStudio - sql

Question

I am trying to use a custom parameter within DataStudio. The data is hosted in BigQuery.
SELECT
timestamp_trunc(o.created_at, #groupby) AS dateMain,
count(o.id) AS total_orders
FROM `x.default.orders` o
group by 1
When I try this, it returns an error saying that "A valid date part name is required at [2:35]"
I basically need to group the dates using a parameter (e.g. day, week, month).
I have also included a screenshot of how I have created the parameter in Google DataStudio. There is a default value set which is "day".

Answer 1

A workaround that might do the trick here is to use a rollup in the group by with the different levels of aggregation of the date, since I am not sure you can pass a DS parameter to work like that.
See the following example for clarity:
with default_orders as (
select timestamp'2021-01-01' as created_at, 1 as id
union all
select timestamp'2021-01-01', 2
union all
select timestamp'2021-01-02', 3
union all
select timestamp'2021-01-03', 4
union all
select timestamp'2021-01-03', 5
union all
select timestamp'2021-01-04', 6
),
final as (
select
count(id) as count_orders,
timestamp_trunc(created_at, day) as days,
timestamp_trunc(created_at, week) as weeks,
timestamp_trunc(created_at, month) as months
from
default_orders
group by
rollup(days, weeks, months)
)
select * from final
The output, then, would be similar to the following:
count | days | weeks | months
------+------------+----------+----------
6 | null | null | null <- this, represents the overall (counted 6 ids)
2 | 2021-01-01| null | null <- this, the 1st rollup level (day)
2 | 2021-01-01|2020-12-27| null <- this, the 1st and 2nd (day, week)
2 | 2021-01-01|2020-12-27|2021-01-01 <- this, all of them
And so on.
At the moment of visualizing this on data studio, you have two options: setting the metric as Avg instead of Sum, because as you can see there's kind of a duplication at each stage of the day column; or doing another step in the query and get rid of nulls, like this:
select
*
from
final
where
days is not null and
weeks is not null and
months is not null