总结

Snowflake 中的数据操作

Jake Roach

Field Data Engineer

Snowflake 中的数据操作

CASE 语句

按条件操控并转换数据。

子查询

在一个查询中复用另一查询的结果。

公用表表达式

为主查询定义临时结果集。

条件逻辑

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;

可以将条件逻辑与聚合函数等组合使用。

子查询

使用子查询以更可读、模块化的方式处理数据的逻辑流程

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;

公用表表达式

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;

公用表表达式（CTE）临时存储查询结果，供后续查询使用

让查询更可读、模块化
可定义并使用多个 CTE

¡Vamos a practicar!

Snowflake 中的数据操作