Ecto union_all with count（*）查询

Question

这是我想要做的：

thirty_days_ago_completed_visits =
  from(v in Visit,
    select: %{a: count("*")},
    where: v.papa_id == ^papa.id,
    where:
      v.scheduled_for >= ^thirty_days_ago and
        v.state in ["completed", "reviewed"]
  )

sixty_days_ago_completed_visits =
  from(v in Visit,
    select: %{b: count("*")},
    where: v.papa_id == ^papa.id,
    where:
      v.scheduled_for >= ^sixty_days_ago and
        v.state in ["completed", "reviewed"]
  )

future_scheduled_visits =
  from(v in Visit,
    select: %{c: count("*")},
    where: v.papa_id == ^papa.id,
    where: v.recurring == false,
    where: v.scheduled_for >= ^Timex.now()
  )

future_recurring_visits =
  from(v in Visit,
    select: %{d: count("*")},
    where: v.papa_id == ^papa.id,
    where: v.recurring == true,
    where: v.scheduled_for >= ^Timex.now()
  )

from(
  a in subquery(thirty_days_ago_completed_visits),
  union_all: ^sixty_days_ago_completed_visits,
  union_all: ^future_scheduled_visits,
  union_all: ^future_recurring_visits
)
|> Repo.all()
|> IO.inspect()

我收到此错误：

**（Ecto.QueryError）子查询/ CTE必须选择源（t），字段（t.field）或地图，在查询中得到：count("*")：

from v0 in PapaPal.Visit,
  where: v0.papa_id == ^"419b3f7f-b74a-42fa-a377-2b7f54886c06",
  where: v0.scheduled_for >= ^#DateTime<2020-04-18 19:31:36.774112Z> and v0.state in ["completed", "reviewed"],
  select: count("*")

我想要做的最后是四个整数，每个查询一个整数-通过对数据库使用单个SQL查询。

任何提示？

Answer 1

Ecto.Query.API.count/1的文档以及错误消息本身，明确指出在将Ecto.Query.API.count/1传递给它时，您必须选择源，字段或地图。下面将工作。

"*"