Question

使用inserted_at列按天/周/月分组行示例：如果在1周之前创建第一行，则按天分组，如果在中间日期未创建任何数据，则将o添加为值。

[
 {"21 Jul" => 12},{"22 Jul" => 0},{"23 Jul" => 3}, {"24 Jul" => 1}...
 {"5 Aug" => 0}
]

提前致谢。

Answer 1

It's not quite clear from the question exactly what is required, but hopefully the following query helps: It will give you the count of records grouped by the date part of inserted_at.

defmodule CountByDateQuery do
  import Ecto.Query

  @doc "to_char function for formatting datetime as dd MON YYYY"
  defmacro to_char(field, format) do
    quote do 
      fragment("to_char(?, ?)", unquote(field), unquote(format))
    end
  end

  @doc "Builds a query with row counts per inserted_at date"
  def row_counts_by_date do
    from record in SomeTable,
    group_by: to_char(record.inserted_at, "dd Mon YYYY"),
    select: {to_char(record.inserted_at, "dd Mon YYYY"), count(record.id)}
  end

end

Usage:

row_counts_by_date() |> Repo.all() |> Map.new()
%{"05 Aug 2017" => 2}

Answer 2

让我们假设您有名为starts_at的带有DateTime字段的事件架构。例如，要获取事件按日期计数的信息，可以使用以下功能：

  def get_events_count_grouped_by_date(query) do
    query
    |> group_by([e], fragment("date(?)", e.starts_at))
    |> select([e], %{date: fragment("date(?)", e.starts_at), count: count(e.id)})
    |> order_by([e], asc: fragment("date(?)", e.starts_at))
  end

然后像这样使用它：

Event |> get_events_count_grouped_by_date() |> Repo.all()

在Elixir中按天/周/月分组行

2 个答案: