3 month rolling COUNT using lookml

Does anyone know how can i get this ?

I want to create rolling 3 month count of a measure .So basically if i want that 3 months to be referred as a single month.

Example : If i want to calculate 3 month MTU count for JULY ,then it should count the measure for MAY,JUNE & JULY. I want this for every month present in the table.

I have this dimension i am using to get month from

dimension_group: created {
type: time
description: “created at date”
timeframes: [
raw,
day_of_month,
time,
date,
week,
month,
quarter,
year
]
sql: ${TABLE}.created_at ;

measure: MTU {
type: count_distinct
description: “MTU”
sql: ${xyz.id} ;;

You can’t do it in the LookML because we can’t put window functions there. The running_count measure is actually not executed as part of the SQL query but at the later stage - client layer. Therefore, you could do it easily with Table Calculation but not LookML