sql - 在PostgreSQL中以两种方式对数据集进行分组

我有一个大的数据集，我需要用两种不同的方式进行分组。我希望能够运行一次查询，这样就不必运行两个单独的查询。
我想使用ROLLUP或GROUPING SETS是可能的，但我必须承认我不完全理解如何使用它们来实现这一点。
这是我要做的一个基本的例子。我试图用一个问题回答的两个问题是：
每家公司每天创建了多少用户？
哪些公司在整个时期内创造了最多的用户？排名前五的公司就足够了。

CREATE TABLE IF NOT EXISTS tmp_users (
    id INTEGER NOT NULL,
    name TEXT NOT NULL,
    created TIMESTAMP NOT NULL,
    companyid INTEGER NOT NULL
);

INSERT INTO tmp_users (id, name, created, companyid)
VALUES
(1, 'Lindsay', '2019-01-01', 1),
(2, 'Michael', '2019-01-02', 1),
(3, 'Stan', '2019-01-04', 3),
(4, 'Gob', '2019-01-04', 1),
(5, 'Buster', '2019-01-01', 1),
(6, 'Lucille', '2019-01-03', 2),
(7, 'Sally', '2019-01-05', 3);

-- Get users created per day, per company
SELECT
    DATE_TRUNC('DAY', created) AS created,
    companyid,
    COUNT(*) AS numberofusers
FROM tmp_users
GROUP BY
    DATE_TRUNC('DAY', created),
    companyid
ORDER BY DATE_TRUNC('DAY', created) DESC;

-- Users per company, with filter
SELECT
    companyid,
    COUNT(*) AS numberofusers
FROM tmp_users
GROUP BY
    companyid
HAVING COUNT(*) > 1
ORDER BY COUNT(*) DESC;

最佳答案

grouping sets可用于在单个选择中返回多个聚合级别：

-- Get users created per day, per company
SELECT *
FROM
 (
   SELECT
      DATE_TRUNC('DAY', created) AS created,
      companyid,
      Count(*) AS numberofusers,
      Row_Number() -- instead of TOP n
      Over (PARTITION BY CASE WHEN DATE_TRUNC('DAY', created) IS NULL THEN 0 ELSE 1 END
            ORDER BY Count(*) DESC) AS rn
   FROM tmp_users
   GROUP BY GROUPING SETS
    (
     (DATE_TRUNC('DAY', created), companyid)  -- daily data
     ,companyid                               -- company data
    )
 ) AS dt
WHERE created IS NOT NULL  -- all daily data
   OR rn <= 5              -- plus the TOP 5 companies
ORDER BY created ASC NULLS FIRST;

见db<>fiddle

关于sql - 在PostgreSQL中以两种方式对数据集进行分组，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/55612571/