sql - 在时间戳上使用 date_trunc 时为 "column must appear in the GROUP BY clause"

Question

我有一个 SQL 查询，它计算具有给定创建日期的联系人。创建日期以毫秒为单位存储为 unix 时间戳，我正在使用 to_timestamp 方法正确格式化它:

SELECT count(*) AS "Count", date_trunc('month', to_timestamp("contacts"."createdate"::double precision / 1000)) AS "Create Date"
FROM "contacts"
GROUP BY "contacts"."createdate"
ORDER BY "contacts"."createdate" ASC

结果如下:

Count | Create Date
-----------------------------------------
1     | Sunday, February 1, 2015 12:00 AM
1     | Sunday, February 1, 2015 12:00 AM
1     | Wednesday, April 1, 2015 12:00 AM
1     | Wednesday, April 1, 2015 12:00 AM
1     | Wednesday, April 1, 2015 12:00 AM

我想按月对它们进行分组，因此对于上面的示例，我希望:

Count | Create Date
-----------------------------------------
2     | February 2015
3     | April 2015

我将 SQL 更改为以下内容:

SELECT count(*) AS "Count", date_trunc('month', to_timestamp("contacts"."createdate"::double precision / 1000)) AS "Create Date"
FROM "contacts"
GROUP BY date_trunc('month', to_timestamp("contacts"."createdate"::double precision / 1000))
ORDER BY "contacts"."createdate" ASC

但是收到一个错误:

ERROR: column "contacts.createdate" must appear in the GROUP BY clause or be used in an aggregate function

有什么办法可以正确地做到这一点？

Answer 1

您可以通过编号引用 SELECT 中的元素:

SELECT count(*) AS "Count", date_trunc('month', to_timestamp("contacts"."createdate"::double precision / 1000)) AS "Create Date"
FROM "contacts"
GROUP BY date_trunc('month', to_timestamp("contacts"."createdate"::double precision / 1000))
ORDER BY 2 ASC