總結！

Snowflake 中的資料操作

Jake Roach

Field Data Engineer

Snowflake 的資料操作

CASE 陳述式

依條件操作並轉換資料。

子查詢（Subqueries）

在一個查詢中運用另一個查詢的結果。

共用資料表運算式

定義暫存結果供主查詢使用。

條件邏輯

SELECT
    todays_date,
    temperature,
    status,
    CASE
        WHEN temperature > 70 AND status NOT IN ('Rain', 'Wind') THEN 'Beach'
        WHEN temperature BETWEEN 45 AND 70 AND status = 'Sun' THEN 'Sports'
        WHEN temperature <= 32 OR status = 'Snow' THEN 'Skiing'
        ELSE 'Stay In'
    END AS activity
FROM weather;

條件邏輯可以與彙總函式等功能結合使用。

子查詢（Subqueries）

以子查詢更可讀、模組化地處理資料的邏輯流程

SELECT
    month_num,
    AVG(differential) AS avg_differential
    MIN(differential) AS most_differential
FROM (
    SELECT
        month_num,
        windchill - temperature AS differential
    FROM weather
    WHERE 
        season = 'Winter' AND
        temperature < 32
)
GROUP BY month_num;

共用資料表運算式

WITH at_risk AS (
    SELECT
        student_id
        course_name,
        teacher_name,
        grade
    FROM student_courses
    WHERE grade < 70 AND is_required
)

SELECT
    students.student_name,
    at_risk.*
FROM at_risk
JOIN students ON at_risk.student_id = students.id;

Common Table Expressions (CTE's) 會暫時儲存查詢結果，供其他查詢後續使用

讓查詢更可讀、模組化
可定義並使用多個 CTE

一起來練習吧！

Snowflake 中的資料操作