TIL - 250127

URL : https://datalemur.com/questions/laptop-mobile-viewership

SELECT
  (
  SELECT count(device_type) 
  FROM viewership 
  WHERE device_type = 'laptop'
  ) laptop_views,
  (
  SELECT count(device_type) 
  FROM viewership 
  WHERE device_type in ('phone','tablet')
  ) mobile_views
;

SELECT만 사용할 수 있다.
처음 알았다.

SELECT 
  SUM(CASE WHEN device_type = 'laptop' THEN 1 ELSE 0 END) AS laptop_views, 
  SUM(CASE WHEN device_type IN ('tablet', 'phone') THEN 1 ELSE 0 END) AS mobile_views 
FROM viewership;

다른 방법도 있다.