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！
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