Transform Array into columns in BigQuery - google-bigquery

Question

I have a json string stored in a string column in BigQuery. There is an Array in it. I would like to pick some fields from array and write its value to BQ columns.
For example - Consider a below json stored in BQ
{
"pool": "mypool",
"statusCode": "0",
"payloads": [
{
"name": "request",
"fullpath": "com.gcp.commontools.edlpayload.EDLPayloadManagerTest$Request",
"jsonPayload": {
"body": "{\"data\":\"foo\"}"
},
"orientation": "REQUEST",
"httpTransport": {
"httpMethod": "POST",
"headers": {
"headers": {
"a": "1"
}
},
"sourceEndpoint": "/v1/foobar"
}
},
{
"name": "response",
"fullpath": "com.gcp.commontools.edlpayload.EDLPayloadManagerTest$Response",
"jsonPayload": {
"body": "{\"data\":\"bar\"}"
},
"orientation": "RESPONSE",
"httpTransport": {
"headers": {
"headers": {
"b": "2"
}
},
"httpResponseCode": 200
}
},
{
"name": "attributes",
"fullpath": "java.util.HashMap",
"nameValuePairs": {
"data": {
"one": "1"
}
},
"orientation": "TRANSITORY"
}
],
"uuid": "11EC-C714-8ADE2390-9619-1B80E63968CC",
"payloadName": "my-overall-name"
}
Consider a target BQ table schema is
pool, requestFullPath, requestPayload, responseFullPath, responsePayload
From the above json, i would like to pick few json elements and map there value to a column in BQ. Please note, array of payload will be dynamic in nature. There can be only 1 payload in the payloads array or there can be multiple. And the order of them is not fixed. For example, request payload can come at [0]th position, 1st position etc.

Answer 1

Consider below
select * from (
select
json_value(json_col, '$.pool') as pool,
json_value(payload, '$.name') as name,
json_value(payload, '$.fullpath') as FullPath,
json_value(payload, '$.jsonPayload.body') as Payload,
from your_table t
, unnest(json_extract_array(json_col, '$.payloads')) payload
)
pivot (any_value(FullPath) as FullPath, any_value(Payload) as Payload for name in ('request', 'response') )
if applied to sample data in your question - output is