Cumulative distinct count

Question

I am working on query to get cumulative distinct count of uids on daily basis.

Example : Say there are 2 uids (100,200) appeared on date 2016-11-01 and they also appea

Answer 1

WITH firstseen AS (
  SELECT uid, MIN(date) date
  FROM sample_table
  GROUP BY 1
)
SELECT DISTINCT date, COUNT(uid) OVER (ORDER BY date) daily_cumulative_count 
FROM firstseen
ORDER BY 1

Using SELECT DISTINCT because (date, COUNT(uid)) will be duplicated many times.

Explanation: for each date dt, it counts uid from the earliest date up to dt, because we are specifying ORDER BY date and it defaults to BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW.