Question

SELECT COUNT(*)
FROM (
    SELECT l.userid
    FROM (
        SELECT DISTINCT userid, CAST(tmstmp AS DATE)
        FROM logins
        WHERE type <> 'mobile'
        AND tmstmp BETWEEN '2013-04-21' AND '2014-04-21') l
    GROUP BY l.userid
    HAVING count(*) > 5) t;

您好，我可以就如何清理此查询提出建议......也许是一种删除其中一个嵌套表的聪明方法？提前谢谢。

Answer 1

听起来您正在寻找另一个aggregate内的aggregate。我认为这是使用单个子查询的最佳选择：

SELECT COUNT(*)
FROM (
    SELECT userid
    FROM logins
    WHERE type <> 'mobile' AND tmstmp BETWEEN '2013-04-21' AND '2014-04-21'
    GROUP BY userid
    HAVING count(distinct CAST(tmstmp AS DATE)) > 5
) t

Answer 2

使用WITH将使其更具可读性：

WITH matching_users AS (
  SELECT userid
  FROM logins
  WHERE type <> 'mobile' AND tmstmp BETWEEN '2013-04-21' AND '2014-04-21'
  GROUP BY userid
  HAVING count(distinct CAST(tmstmp AS DATE)) > 5
)
SELECT count(*) FROM matching_users

Answer 3

这是一种方法：

SELECT COUNT(*)
FROM (
SELECT userid, COUNT(DISTINCT CAST(tmstmp AS DATE)) as number_of_logins
FROM logins l
WHERE type <> 'mobile' AND tmstmp BETWEEN '2013-04-21' AND '2014-04-21'
GROUP BY l.userid
HAVING number_of_logins > 5) t

这会获取登录日期的不同日期，并仅计算超过5的用户

使用嵌套表清理SQL查询

3 个答案: