Unnest Multiple level nested fields in BigQuery

Bigquery supports denormalized data with repeated structures. To access the table with nested structures use UNNEST command.

Example: Here's a sample table

Here is an example query that attempt to unnest changelog.histories or changelog.histories.items result in the below error.

SELECT changelog.histories.items.to\nFROM jirasparta_database.jira_issues, \n     unnest(changelog.histories) \n

Error: Cannot access field items on a value with type ARRAY, ...>, \nitems ARRAYto STRING, field STRING, fieldtype STRING, ...>>, ...>> at [1:28]

Solution:

You will have to unnest the column as shown below:

SELECT item.to   \nFROM jirasparta_database.jira_issues, \nUNNEST(changelog.histories) history, UNNEST(history.items) item

dan-irving

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