Unnesting structs in BigQuery

问题

What is the correct way to flatten a struct of two arrays in BigQuery? I have a dataset like the one pictured here (the struct.destination and struct.visitors arrays are ordered - i.e. the visitor counts correspond specifically to the destinations in the same row):

I want to reorganize the data so that I have a total visitor count for each unique combination of origins and destinations. Ideally, the end result will look like this:

I tried using UNNEST twice in a row - once on struct.destination and then on struct.visitors, but this produces the wrong result (each destination gets mapped to every value in the array of visitor counts when it should only get mapped to the value in the same row):

SELECT
  origin,
  unnested_destination,
  unnested_visitors
FROM
  dataset.table,
  UNNEST(struct.destination) AS unnested_destination,
  UNNEST(struct.visitors) AS unnested_visitors

回答1:

You have one struct that is repeated. So, I think you want:

SELECT origin,
       s.destination,
       s.visitors
FROM dataset.table t CROSS JOIN
     UNNEST(t.struct) s;

EDIT:

I see, you have a struct of two arrays. You can do:

SELECT origin, d.destination, v.visitors
FROM dataset.table t CROSS JOIN
     UNNEST(struct.destination) s WITH OFFSET nd LEFT JOIN
     UNNEST(struct.visitors) v WITH OFFSET nv
     ON nd = nv

来源：https://stackoverflow.com/questions/58920800/unnesting-structs-in-bigquery