Mellanliggande aggregatfunktioner

Automatisering av datapipelines i Snowflake

Emily Melhuish

Technical Curriculum Developer, Snowflake

Körordning

Order of operations.png

SQL körs inte i den ordning det skrivs

Rader: bygg datamängden
Grupper: sammanfatta den
Resultat: forma utdata

¹ * Snowflake Learning Material

Vanliga aggregatfunktioner

COUNT(*) / COUNT(DISTINCT col) — totalt antal rader; unika värden
SUM — kolumnsumma
AVG — medelvärde
MIN / MAX — intervall

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;

Problemet med flera frågor

Användning per region och lager

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

Delsummor per region

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

Total användning

SELECT 
SUM(credits_used) 
FROM usage;

GROUPING SETS

Indata

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

Utdata

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

Obs: Ge NULL-värden betydelse via CASE-sats

ROLLUP

Indata

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

Utdata

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

Indata

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

Utdata

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() och 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);

Skärmbild av tabellutdata i markdown

Låt oss öva!

Automatisering av datapipelines i Snowflake