Funcții de agregare intermediare

Automatizarea pipeline-urilor de date în Snowflake

Emily Melhuish

Technical Curriculum Developer, Snowflake

Ordinea operațiilor

Order of operations.png

SQL nu se execută în ordinea în care este scris

Rânduri: construirea setului de date
Grupuri: rezumarea datelor
Rezultat: formatarea ieșirii

¹ * Snowflake Learning Material

Funcții de agregare comune

COUNT(*) / COUNT(DISTINCT col) — total rânduri; valori unice
SUM — total coloană
AVG — valoare medie
MIN / MAX — interval

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;

Problema interogărilor multiple

Utilizare pe regiune și depozit

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

Subtotaluri pe regiune

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

Total general

SELECT 
SUM(credits_used) 
FROM usage;

GROUPING SETS

Intrare

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

Ieșire

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

Notă: Adăugați semnificație valorilor NULL prin instrucțiunea CASE

ROLLUP

Intrare

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

Ieșire

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

Intrare

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

Ieșire

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() și 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);

Captură de ecran a ieșirii tabelului markdown

Să exersăm!

Automatizarea pipeline-urilor de date în Snowflake