將SQL查詢轉換爲ActiveRecord關係

Question

如何將以下SQL查詢轉換爲ActiveRecord關係，以便可以使用範圍對其進行擴展？

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 

這是我要嘗試直ARel嗎？

我試過把它分解成作用域/子查詢，但子查詢上的選擇最終在封閉查詢中，因此拋出PostgreSql錯誤，因爲在GROUP BY或ORDER BY中未指定列聲明。

更新： 你假設它是PostgreSQL是正確的。我嘗試了你的查詢，但是它爲直接查詢和ActiveRecord等價物拋出了一個PG::Error: ERROR: column "rownum" does not exist。

但是，當我將查詢包裝在單獨的查詢中時，它起作用。我假設ROW_NUMBER（）直到select被投影到數據集之後才被創建。所以下面的查詢工作：

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 

我已經成功地按摩到以下幾點：

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，這是非常哈克，是一個龐大的代碼味道。任何想法如何重構？

Answer 1

你顯然正試圖獲得最新的鍛鍊（最高id）的細節，匹配每個用戶的最高權重。它也似乎是你正在使用PostgreSQL（MySQL沒有CTE的），糾正我，如果我錯了。

如果是這樣，你可以利用窗口函數，並簡化您的查詢：

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的可以寫爲：

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")