ecto 片段作为查询源

Question

我正在尝试做这样的事情：

SELECT days.date, SUM(tes.duration) FROM (
  SELECT 
      DATE_FORMAT(
          now() - INTERVAL (@num := @num + 1) DAY,
          '%Y-%m-%d'
      ) date
  FROM time_entries, (SELECT @num:=-1) num
  LIMIT 31
) AS days
LEFT JOIN (
  SELECT te.duration, DATE_FORMAT(te.date, '%Y-%m-%d') date
  FROM time_entries AS te
  WHERE te.account_id = 50150 AND te.deleted_at IS NULL
) AS tes ON tes.date = days.date
GROUP BY days.date
ORDER BY days.date

但这在 ecto 中似乎是不可能的。我正在尝试这个：

from(
  # creates 30 rows for each date 30 days into the past
  days in subquery(
    from(
      num in "time_entries, (SELECT @num := -1)",
      select: %{
        date: fragment("DATE_FORMAT(NOW() - INTERVAL (@num := @num + 1) DAY, '%Y-%m-%d')")
      }
    )
  ),
  # join each date with time entries on this account and sub duration for each day
  left_join: tes in subquery(
    from(
      # using time_entries__undeleted was really slow for some reason… need to look into that
      te in "time_entries",
      select: %{
        duration: te.duration,
        date: fragment("DATE_FORMAT(?, '%Y-%m-%d')", te.date),
        where: te.account_id == ^user.account_id
      },
    )
  ), on: tes.date == days.date,
  group_by: days.date,
  order_by: days.date
)

但我得到了错误：

(Mariaex.Error) (1146): Table 'development.time_entries, (select @num := -1)' doesn't exist

我需要在此查询之上动态撰写，所以我不想求助于Ecto.Adapters.SQL.query!。有什么想法吗？

Answer 1

您不能那样做，但是语法 SELECT … FROM a, b … 大致相当于 Ecto 支持的 SELECT … FROM a CROSS JOIN b …。所以你需要的是

from entry in "time_entries",
  cross_join: num in fragment("(SELECT @num = -1)"),
  …