高度な共通テーブル式

Snowflake でのデータ操作

Jake Roach

Field Data Engineer

複数の共通テーブル式を定義する

1つの WITH 句で複数の共通テーブル式を定義できます

任意の数のCTEを定義可能
CTE同士をJOINできる
CTE内で複雑な処理も可能
あるCTEの結果を別のCTEで利用可能

WITH <cte-name> AS (

    <query>

), <another-cte-name> (

    -- Add another query!
    <another-query>
)

-- These CTE's could be JOIN'd 
SELECT ... ;

成績上位のコース

WITH active_courses AS (
    SELECT
        id,
        course_name,
        teacher_name
    FROM courses
    WHERE is_active

), course_avgs (
    SELECT
        course_id,
        AVG(grade) AS avg_grade
    FROM student_courses
    GROUP BY course_id
)


SELECT
    a.course_name,
    a.teacher_name,
    c.avg_grade
FROM active_courses AS a

-- JOIN these CTEs together
JOIN course_avgs AS c
    ON a.id = c.course_id

ORDER BY avg_grade DESC;

クエリの可読性が向上！

成績上位のコース

各コースの平均得点と教員名の最終出力を構成する一時結果セット

在職教員

WITH active_courses AS (
    SELECT
        id,
        course_name,
        teacher_name,
        teacher_tenure
    FROM courses

    -- JOIN the teachers table to the courses 
    -- table to get teacher_tenure
    JOIN teachers 
        ON courses.teacher_id = teachers.id

    WHERE is_active
), 
...

...
), course_avgs (
    SELECT
        course_id,
        AVG(grade) AS avg_grade
    FROM student_courses
    GROUP BY course_id
)


SELECT
    a.teacher_name,
    a.teacher_tenure
    MAX(c.avg_grade) AS highest_grade
FROM active_courses AS a
JOIN course_avgs AS c ON a.id = c.course_id
GROUP BY a.teacher_name, a.teacher_tenure;

在職教員

教員の在職年数と各自の最高コース平均を求めるクエリの結果セット

練習しましょう！

Snowflake でのデータ操作