SQL 子查询使用主查询中的 group by item

Question

我有一个 table，带有 created 时间戳和 id 标识符。

我每周可以获得独特 id 的数量：

SELECT date_trunc('week', created)::date AS week, count(distinct id) 
FROM my_table
GROUP BY week ORDER BY week;

现在我想通过独特的 id 获得每周 created 的累计数量，如下所示：

SELECT date_trunc('week', created)::date AS week, count(distinct id),
       (SELECT count(distinct id)
        FROM my_table
        WHERE date_trunc('week', created)::date <= week) as acc
FROM my_table
GROUP BY week ORDER BY week;

但这不起作用，因为 week 在子 select (ERROR: column "week" does not exist) 中不可访问。

我该如何解决这个问题？

我正在使用 PostgreSQL

Answer 1

使用累积聚合。但是，我认为您不需要 distinct，所以：

SELECT date_trunc('week', created)::date AS week, count(*) as cnt,
       SUM(COUNT(*)) OVER (ORDER BY MIN(created)) as running_cnt
FROM my_table
GROUP BY week
ORDER BY week;

在任何情况下，正如您所描述的问题，您可以将 cnt 更改为使用 count(distinct)。您的子查询根本没有使用 distinct。

Answer 2

CTE 或临时 table 应该可以解决您的问题。这是一个使用 CTE 的示例。

 WITH abc AS (
     SELECT date_trunc('week', created)::date AS week, count(distinct id) as IDCount
     FROM my_table
     GROUP BY week ORDER BY week;
 )

SELECT abc.week, abc.IDcount,
       (SELECT count(*)
        FROM my_table
        WHERE date_trunc('week', created)::date <= adc.week) as acc
FROM abc
GROUP BY week ORDER BY abc.week;

希望对您有所帮助

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