打开SQL查询到ActiveRecord的关系(Turn SQL query into Active

我怎样才能把下面的SQL查询到一个ActiveRecord的关系，这样我可以在其上扩大与范围？

WITH joined_table AS (
    SELECT workout_sets.weight AS weight, 
        workouts.user_id AS user_id, 
        workouts.id AS workout_id, 
        workout_sets.id AS workout_set_id,
        workout_exercises.exercise_id AS exercise_id
    FROM workouts 
    INNER JOIN workout_exercises ON workout_exercises.workout_id = workouts.id 
    INNER JOIN workout_sets ON workout_sets.workout_exercise_id = workout_exercises.id       
    ORDER BY workout_sets.weight DESC
    ),

sub_query AS (
    SELECT p.user_id, MAX(weight) as weight
        FROM joined_table p
            GROUP BY p.user_id
),

result_set AS (
    SELECT MAX(x.workout_id) AS workout_id, x.user_id, x.weight, x.workout_set_id, x.exercise_id
    FROM joined_table x
    JOIN sub_query y 
    ON y.user_id = x.user_id AND y.weight = x.weight
    GROUP BY x.user_id, x.weight, x.workout_set_id, x.exercise_id
    ORDER BY x.weight DESC)

SELECT workouts.*, result_set.weight, result_set.workout_set_id, result_set.exercise_id
FROM workouts, result_set
WHERE workouts.id = result_set.workout_id

这是不是我会直AREL尝试？

我试着将其分成范围/子查询，但在子查询的选择在封闭的查询结束，从而因为在封闭的语句分组依据或ORDER BYS没有指定列抛出PostgreSQL的错误。

更新：你在你的假设是正确的PostgreSQL。我试图您的查询，但它抛出一个PG::Error: ERROR: column "rownum" does not exist ，对于直查询和ActiveRecord的等价。

然而，当我在一个单独的查询包裹查询，它的工作原理。我假设的ROW_NUMBER（）没有得到，直到选择投射到数据集之后创建的。所以下面的查询工作：

SELECT workouts.*, t.weight, t.workout_set_id, t.exercise_id, t.row_num
FROM workouts,
(SELECT workouts.id as workout_id, workout_sets.weight as weight,
                workout_sets.id AS workout_set_id,
                   workout_exercises.id AS exercise_id,
                   ROW_NUMBER() OVER ( 
            PARTITION BY workouts.user_id 
            ORDER BY workout_sets.weight DESC, workouts.id DESC ) row_num
     FROM workouts
     JOIN workout_exercises ON workout_exercises.workout_id = workouts.id 
     JOIN workout_sets ON workout_sets.workout_exercise_id = workout_exercises.id) as t
WHERE workouts.id = t.workout_id AND t.row_num = 1

我已经成功地按摩到以下几点：

  selected_fields = <<-SELECT
    workouts.id AS workout_id, 
    workout_sets.weight AS weight,
    workout_sets.id AS workout_set_id,
    workout_exercises.id AS exercise_id,
    ROW_NUMBER() OVER (
       PARTITION BY workouts.user_id 
       ORDER BY workout_sets.weight DESC, workouts.id DESC) as row_num
  SELECT

  Workout.joins(", (#{Workout.joins(:workout_exercises => :workout_sets).select(selected_fields).to_sql}) as t").select("workouts.*, t.*").where("workouts.id = t.workout_id AND t.row_num = 1").order("t.weight DESC")

但是，正如你所知道的，这是非常哈克，是一个庞大的代码味道。任何想法，如何重构呢？

您显然是想拿到赛最高的权重为每个用户，最新的锻炼（最高ID）的详细信息。还可以看出你正在使用PostgreSQL（MySQL没有CTE的），纠正我，如果我错了这一点。

如果是这样，你可以使用窗口功能，简化您的查询：

SELECT * FROM (
  SELECT workouts.*, workout_sets.weight,
                     workout_sets.id AS workout_set_id,
                     workout_exercises.id AS exercise_id,
                     ROW_NUMBER() OVER (
                         PARTITION BY workouts.user_id 
                         ORDER BY workout_sets.weight DESC, workouts.id DESC ) as rowNum
  FROM workouts
  JOIN workout_exercises ON workout_exercises.workout_id = workouts.id 
  JOIN workout_sets ON workout_sets.workout_exercise_id = workout_exercises.id
) t
WHERE rowNum = 1

这在ActiveRecord的可以写为：

selected_fields = <<-SELECT
  workouts.*, 
  workout_sets.weight,
  workout_sets.id AS workout_set_id,
  workout_exercises.id AS exercise_id,
  ROW_NUMBER() OVER (
     PARTITION BY workouts.user_id 
     ORDER BY workout_sets.weight DESC, workouts.id DESC) as rowNum
SELECT

subquery = Workout.joins(:workout_exercises => :workout_sets).
                   select(selected_fields).to_sql
Workout.select("*").from(Arel.sql("(#{subquery}) as t"))
       .where("rowNum = 1")