Funções de agregação intermediárias

Automação de Pipelines de Dados no Snowflake

Emily Melhuish

Technical Curriculum Developer, Snowflake

Ordem de execução

Ordem de execução.png

O SQL não roda na ordem que você escreve

Linhas: monte o dataset
Grupos: resuma
Resultado: molde a saída

¹ * Snowflake Learning Material

Funções de agregação comuns

COUNT(*) / COUNT(DISTINCT col) — linhas totais; valores únicos
SUM — total da coluna
AVG — média
MIN / MAX — intervalo

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;

O problema com várias consultas

Retornar uso por região e warehouse

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

Retornar subtotais por região

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

Retornar total geral

SELECT 
SUM(credits_used) 
FROM usage;

GROUPING SETS

Entrada

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

Saída

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

Observação: Dê significado aos NULLs com CASE

ROLLUP

Entrada

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

Saída

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

Entrada

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

Saída

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() e 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);

Captura de tela da saída da tabela em markdown

Vamos praticar!

Automação de Pipelines de Dados no Snowflake