TIL - 250202

리뷰 : WHERE절에 넣을지 ON절에 넣을지 잘 생각하자.

URL : https://datalemur.com/questions/sql-ibm-db2-product-analytics

SELECT
  cnt
  ,count(employee_id)
FROM (
  SELECT
    e.employee_id
    ,COUNT(DISTINCT query_id) cnt
  FROM employees e 
  LEFT JOIN queries q 
  ON e.employee_id = q.employee_id
  AND EXTRACT(QUARTER FROM query_starttime) = 3
  GROUP BY 1
) a
GROUP BY 1
ORDER BY 1
;