Fungsi Window

Otomatisasi Data Pipeline di Snowflake

Emily Melhuish

Technical Curriculum Developer, Snowflake

Apa itu Fungsi Window?

Hitung lintas baris tanpa menggabungkannya

Menghasilkan nilai per baris memakai himpunan di sekitarnya — window-nya
Berbeda dari GROUP BY: setiap baris masuk, setiap baris keluar
Ditetapkan oleh klausa OVER

3 kategori utama:

Peringkat: ROW_NUMBER(), RANK(), DENSE_RANK()
Agregasi: SUM(), AVG(), COUNT() with OVER()
Navigasi: LAG(), LEAD(), FIRST_VALUE(), LAST_VALUE()

Info lebih lanjut di kursus DataCamp Window Functions in Snowflake

Klausa OVER()

SELECT shipment_id
, region
, delivery_days
, AVG(delivery_days) 
    OVER ( PARTITION BY region ORDER BY dispatched_at ) AS avg_days_in_region 
FROM shipments;

SHIPMENT_ID	REGION	DELIVERY_DAYS	RUNNING_AVG_DAYS_IN_REGION
SHP-001	EMEA	3	3.00
SHP-002	EMEA	5	4.00
SHP-003	EMEA	4	4.00
SHP-004	APAC	6	6.00

ROW_NUMBER vs RANK vs DENSE_RANK

SELECT
    shipment_id AS shipment, delivery_days AS days,
    ROW_NUMBER() OVER (ORDER BY delivery_days) AS row_number,
    RANK()       OVER (ORDER BY delivery_days) AS rank,
    DENSE_RANK() OVER (ORDER BY delivery_days) AS dense_rank
FROM shipments ORDER BY delivery_days;

SHIPMENT	DELIVERY_DAYS	ROW_NUMBER	RANK	DENSE_RANK
SHP-001	3	1	1	1
SHP-002	5	2	2	2
SHP-003	5	3	2	2
SHP-004	7	4	4	3

LAG dan LEAD

Input

Input SQL Lag dan Lead

Output

Output Lag dan Lead

Total Berjalan dan Rata-Rata Bergulir

Bingkai ROWS vs RANGE

ROWS BETWEEN: menghitung posisi baris fisik — offset tepat terlepas dari nilai

-- ROWS: selalu memilih tepat N baris fisik sebelumnya
SUM(credits) OVER (ORDER BY month ROWS BETWEEN 2 PRECEDING AND CURRENT ROW)
-- Termasuk baris saat ini dan dua sebelumnya

RANGE BETWEEN: memakai nilai, mengelompokkan baris dengan nilai ORDER BY yang sama

-- RANGE: menyertakan semua baris yang seri pada nilai batas
SUM(credits) OVER (ORDER BY month RANGE BETWEEN 2 PRECEDING AND CURRENT ROW)

Gunakan Range hanya bila logika berbasis batas nilai

Ayo berlatih!

Otomatisasi Data Pipeline di Snowflake