How to create new table with nested schema entirely in BigQuery - sql

Question

I've got a nested table A in BigQuery with a schema as follows:
{
"name": "page_event",
"mode": "repeated",
"type": "RECORD",
"fields": [
{
"name": "id",
"type": "STRING"
}
]
}
I would like to enrich table A with data from other table and save result as a new nested table. Let's say I would like to add "description" field to table A (creating table B), so my schema will be as follows:
{
"name": "page_event",
"mode": "repeated",
"type": "RECORD",
"fields": [
{
"name": "id",
"type": "STRING"
},
{
"name": "description",
"type": "STRING"
}
]
}
How do I do this in BigQuery? It seems, that there are no functions for creating nested structures in BigQuery SQL (except NEST functions, which produces a list - but this function doesn't seem to work, failing with Unexpected error)
The only way of doing this I can think of, is to:
use string concatenation functions to produce table B with single field called "json" with content being enriched data from A, converted to json string
export B to GCS as set of files F
load F as table C
Is there an easier way to do it?

Answer 1

To enrich schema of existing table one can use tables patch API
https://cloud.google.com/bigquery/docs/reference/v2/tables/patch
Request will look like below
PATCH https://www.googleapis.com/bigquery/v2/projects/{project_id}/datasets/{dataset_id}/tables/{table_id}?key={YOUR_API_KEY}
{
"schema": {
"fields": [
{
"name": "page_event",
"mode": "repeated",
"type": "RECORD",
"fields": [
{
"name": "id",
"type": "STRING"
},
{
"name": "description",
"type": "STRING"
}
]
}
]
}
}
Before Patch
After Patch