Particionar datos en una función de ventana

Funciones de ventana en Snowflake

Jake Roach

Field Data Engineer

Clasificar datos

Aquí estamos clasificando todos los registros del resultado.

      user_id  |    event_name   |  km_traveled  |  closest_attendees 
      -------  | --------------- | ------------- | ----------------- 
      user_81  |  Lunar Drift    |      0.5      |         1         
      user_02  |  Lunar Drift    |      1.1      |         2       
      user_33  |  Crimson Arc    |      8.6      |         3          
      user_33  |  Neon Prophet   |      8.6      |         3         
      user_15  |  VibeStorm      |      17       |         5          
      user_94  |  The Dusk Owls  |      41       |         6        
      user_47  |  Lunar Drift    |      61       |         7   
      user_56  |  Crimson Arc    |      116      |         8

Clasificar con particiones

Ahora queremos clasificar datos en cada ventana.

Una tabla que clasifica a los asistentes según la distancia recorrida a cada recinto

PARTITION BY

SELECT
    user_id,
    event_name,
    distance_traveled,

    RANK() OVER(
        -- Crear ventana por event_name
        PARTITION BY event_name
        ORDER BY km_traveled
    ) AS closest_concert_goer

FROM CONCERTS.attendance;

PARTITION BY crea ventanas de registros para aplicar funciones

PARTITION BY va antes de ORDER BY en OVER(...)
Similar a GROUP BY, pero no "colapsa" registros

Clasificar con particiones

SELECT
    level,
    price,

    RANK() OVER(
        PARTITION BY level
        ORDER BY price DESC
    ) AS price_rank

FROM CONCERTS.attendance;

PARTITION BY crea ventanas

      level  |   price   | price_rank 
    -------- | --------- | -----------
       100   |    765    |      1
       100   |    617    |      2
       100   |    490    |      3
       100   |    490    |      3

                  ...

       200   |    212    |      1
       200   |    207    |      2

                  ...

Generar métricas resumen con FIRST_VALUE

    FIRST_VALUE(<1>) OVER(
        PARTITION BY <2>
        ORDER BY <3>
    ) AS <alias>

FIRST_VALUE devuelve el primer valor en una ventana

<1>: columna a devolver

<2>: campo para particionar

<3>: campo que determina el primer registro

Generar métricas resumen con AVG

AVG(<1>) OVER(
    PARTITION BY <2>
    -- No need to ORDER BY!
) AS <alias>

AVG calcula la media de un campo en cada ventana

<1>: columna para promediar

<2>: campo para particionar

... no hace falta ORDER BY

Satisfacción del cliente

SELECT
    user_id, event_name, satisfaction_score,


    FIRST_VALUE(satisfaction_score) OVER(
        PARTITION BY event_name   -- Puntuación del asistente más cercano
        ORDER BY km_traveled
    ) AS first_score,


    -- Media de satisfacción en la "ventana" de registros
    AVG(satisfaction_score) OVER(
        PARTITION BY event_name
    ) AS average_score


FROM CONCERTS.attendance;

Satisfacción del cliente


      user_id  |   event_name   |  satisfaction_score  |  first_score  |  average_score 
     --------- | -------------- | -------------------- | ------------- | ---------------

      user_26  |  Pulse Theory  |          71          |       98      |      84.5      
      user_92  |  Pulse Theory  |          98          |       98      |      84.5      

                                          ...

      user_57  |   Nova Sway    |           4          |       22      |      29.3      
      user_39  |   Nova Sway    |          22          |       22      |      29.3      
      user_44  |   Nova Sway    |          62          |       22      |      29.3      

                                          ...

¡Vamos a practicar!

Funciones de ventana en Snowflake