题解 | SQL 190. 某乎问答11月份日人均回答量

WITH t1 AS (
    SELECT answer_date,
           ROUND(
               count(author_id)
                   /
               count(DISTINCT author_id)
               , 2)
             AS per_num
           FROM
    answer_tb
    WHERE SUBSTR(answer_date,6,2) = '11'
    GROUP BY answer_date
    ORDER BY answer_date ASC
)
SELECT * FROM t1;

# 这道题指的是计数以及去重！