按星期几组

Question

我有一个conversations带有inserted_at列的表

我想绘制一个图表,显示conversations随时间创建的数量.

我希望能够按日期,星期几和日期时间对数据进行分组,以显示可能的趋势.

我将使用7天,1个月和6个月的间隔.

例:

间隔:1 month分组day of week

我喜欢类似的东西

| Monday | Tuesday | Wednesday | Thursday | Friday |
|--------|---------|-----------|----------|--------|
| 11     | 22      | 19        | 17       | 10     |

或间隔:7 days分组依据date

| 1/1 | 2/1 | 3/1 | 4/1 | 5/1 | 6/1 | 7/1 |
|-----|-----|-----|-----|-----|-----|-----|
| 11  | 22  | 19  | 17  | 10  | 10  | 7   |

实现这一目标的最佳方法是什么(非常感谢示例),PostgreSQL是否适合这类查询？

最后,是否有任何特殊的索引可以改善此类查询？

Answer 1

一周中的日子:

select
    count(extract(dow from inserted_at) = 1 or null) as monday,
    count(extract(dow from inserted_at) = 2 or null) as tuesday,
    count(extract(dow from inserted_at) = 3 or null) as wednesday,
    count(extract(dow from inserted_at) = 4 or null) as thursday,
    count(extract(dow from inserted_at) = 5 or null) as friday,
from conversations

count只计算not null值.false or null是null这样只会true被计算在内.

在较新的版本中有一个聚合filter:

count(*) filter (where extract(dow from inserted_at) = 4) as thursday