将SQL查询转换为ActiveRecord关系

Question

如何将以下SQL查询转换为ActiveRecord关系，以便可以使用范围对其进行扩展？

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 

这是我要尝试直ARel吗？

我试过把它分解成作用域/子查询，但子查询上的选择最终在封闭查询中，因此抛出PostgreSql错误，因为在GROUP BY或ORDER BY中未指定列声明。

更新： 你假设它是PostgreSQL是正确的。我尝试了你的查询，但是它为直接查询和ActiveRecord等价物抛出了一个PG::Error: ERROR: column "rownum" does not exist。

但是，当我将查询包装在单独的查询中时，它起作用。我假设ROW_NUMBER（）直到select被投影到数据集之后才被创建。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？

Answer 1

你显然正试图获得最新的锻炼（最高id）的细节，匹配每个用户的最高权重。它也似乎是你正在使用PostgreSQL（MySQL没有CTE的），纠正我，如果我错了。

如果是这样，你可以利用窗口函数，并简化您的查询：

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 

其中在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")