How to create nested JSON format table from flat table in BigQuery?

Question

I have a wide flat table, stored in Google bigquery in the folowing similar format :

log_date:integer,sessionid:integer,computer:string,ip:string,event_id:integer,amount:float

I'm trying to create this table in hierarchical nested format , having 2 nested levels , as following :

 [
  {
    "name": "log_date",
    "type": "integer"
  }, 
  {
    "name": "session",
    "type": "record",
    "mode": "repeated",
    "fields": [                 
     {
       "name": "sessionid",
       "type": "integer"
         },
     {
       "name": "computer",
       "type": "string"
        },
        {
       "name": "ip",
       "type": "string"
        },
        {
    "name": "event",
    "type": "record",
    "mode": "repeated",
    "fields": [
    {
       "name": "event_id",
       "type": "integer"
     },
     {
       "name": "amount",
       "type": "float"
     }]] } ]

What is the best way to generate the json formatted data file from bigquery table ? Is there a different and faster approach than 1. download the table into external csv 2. build the json record , and write it into external file 3. upload the external json file into new bigquery table

Can we have a direct process that generates json from existing tables ?

Thank you , H

Answer 1

There isn't currently a way to automatically transform the data to a nested format. If you'd like to get the data out in json format rather than CSV, you can use the export commend with the --destination_format flag set to NEWLINE_DELIMITED_JSON. e.g.

bq extract \
    --destination_format=NEWLINE_DELIMITED_JSON \
    yourdataset.table \
    gs://your_bucket/result*.json