Intermediaire aggregatiefuncties

Automatisering van datapijplijnen in Snowflake

Emily Melhuish

Technical Curriculum Developer, Snowflake

Volgorde van bewerkingen

Volgorde van bewerkingen.png

SQL draait niet in de volgorde waarin je het schrijft

Rijen: stel de dataset samen
Groepen: vat samen
Resultaat: vorm de output

¹ * Snowflake Learning Material

Veelgebruikte aggregaatfuncties

COUNT(*) / COUNT(DISTINCT col) — totaal rijen; unieke waarden
SUM — kolomsom
AVG — gemiddelde
MIN / MAX — bereik

SELECT COUNT(*) AS total_shipments,
       COUNT(DISTINCT carrier_id) AS unique_carriers,
       SUM(delivery_days) AS total_days,
       AVG(delivery_days) AS avg_days
FROM shipments;

Het probleem met meerdere queries

Gebruik per regio en warehouse

SELECT 
region
, warehouse_name
, SUM(credits_used) 
FROM usage 
GROUP BY region, warehouse_name;

Subtotaal per regio

SELECT region
, SUM(credits_used) 
FROM usage GROUP BY region;

Totaal gebruik

SELECT 
SUM(credits_used) 
FROM usage;

GROUPING SETS

Input

SELECT region
, warehouse_name
, SUM(credits_used) AS total 
FROM usage 
GROUP BY GROUPING SETS ( 
  (region, warehouse_name)
  , (region)
  , () 
);

Output

REGION	WAREHOUSE_NAME	TOTAL
EMEA	harbr_wh_prod	1240.50
EMEA	harbr_wh_dev	380.00
EMEA	NULL	1620.50
APAC	harbr_wh_prod	890.25
APAC	NULL	890.25
NULL	NULL	2510.75

Opmerking: Geef betekenis aan NULLs via een CASE-statement

ROLLUP

Input

SELECT 
region
, warehouse_name
, SUM(credits_used) AS total 
FROM usage 
GROUP BY ROLLUP (region, warehouse_name);

Output

REGION	WAREHOUSE_NAME	TOTAL
EMEA	harbr_wh_prod	1240.50
EMEA	harbr_wh_dev	380.00
EMEA	NULL	1620.50
APAC	harbr_wh_prod	890.25
APAC	NULL	890.25
NULL	NULL	2510.75

CUBE

Input

SELECT 
region
, warehouse_name
, SUM(credits_used) AS total
FROM usage 
GROUP BY CUBE (region, warehouse_name);

Output

REGION	WAREHOUSE_NAME	TOTAL
EMEA	harbr_wh_prod	1240.50
EMEA	harbr_wh_dev	380.00
EMEA	NULL	1620.50
APAC	harbr_wh_prod	890.25
APAC	NULL	890.25	}
NULL	harbr_wh_prod	2130.75
NULL	harbr_wh_dev	380.00
NULL	NULL	2510.75

GROUPING() en GROUPING_ID()

SELECT region, warehouse_name, SUM(credits_used) AS total_credits, GROUPING(region) AS is_region_agg, GROUPING(warehouse_name) AS is_wh_agg , 
GROUPING_ID(region, warehouse_name) AS grouping_level 
FROM usage 
GROUP BY ROLLUP (region, warehouse_name);

Schermafbeelding van markdown-tabeloutput

Laten we oefenen!

Automatisering van datapijplijnen in Snowflake