How to generate CREATE TABLE script from an existing table - google-bigquery

Question

I create a table with Big Query interface. A large table. And I would like to export the schema of this table in Standard SQL (or Legacy SQL) syntax.
Is it possible ?
Thanks !

Answer 1

You can get the DDL for a table with this query:
SELECT t.ddl
FROM `your_project.dataset.INFORMATION_SCHEMA.TABLES` t
WHERE t.table_name = 'your_table_name'
;

Answer 2

As can be read in this question it is not possible to do so and there is a feature request to obtain the output schema of a standard SQL query but seems like it was not finally implemented. Depending on what your use case is, apart from using bq, another workaround is to do a query with LIMIT 0. Results are returned immediately (tested with a 100B row table) with the schema field names and types.
Knowing this you could also automate the procedure in your favorite scripting language. As an example I used Cloud Shell as the CLI and API calls. It makes three successive calls where the first one executes the query and a jobId is obtained (unnecessary fields are not included in request URL), then we obtain the dataset and table IDs correspondent to that particular job and, finally, the schema is retrieved.
I used the jq tool to parse the responses (manual), which comes preinstalled in the Shell, and wrapped everything in a shell function:
result_schema()
{
QUERY=$1
authToken="$(gcloud auth print-access-token)"
projectId=$(gcloud config get-value project 2>\dev\null)
# get the jobId
jobId=$(curl -H"Authorization: Bearer $authToken" \
-H"Content-Type: application/json" \
https://www.googleapis.com/bigquery/v2/projects/$projectId/queries?fields=jobReference%2FjobId \
-d"$( echo "{
\"query\": "\""$QUERY" limit 0\"",
\"useLegacySql\": false
}")" 2>\dev\null|jq -j .jobReference.jobId)
# get destination table
read -r datasetId tableId <<< $(curl -H"Authorization: Bearer $authToken" \
"https://www.googleapis.com/bigquery/v2/projects/$projectId/jobs/$jobId?fields=configuration(query(destinationTable(datasetId%2CtableId)))" 2>\dev\null | jq -j '.configuration.query.destinationTable.datasetId, " " ,.configuration.query.destinationTable.tableId')
# get resulting schema
curl -H"Authorization: Bearer $authToken" https://www.googleapis.com/bigquery/v2/projects/$projectId/datasets/$datasetId/tables/$tableId?fields=schema 2>\dev\null | jq .schema.fields
}
then we can invoke the function by querying a 100B row public dataset (don't specify LIMIT 0 as the function automatically adds it):
result_schema 'SELECT year, month, CAST(wikimedia_project as bytes) AS project_bytes, language AS lang FROM `bigquery-samples.wikipedia_benchmark.Wiki100B` GROUP BY year, month, wikimedia_project, language'
with the following output as the schema (mind the selected fields using casts and aliases to modify the returned schema):
[
{
"name": "year",
"type": "INTEGER",
"mode": "NULLABLE"
},
{
"name": "month",
"type": "INTEGER",
"mode": "NULLABLE"
},
{
"name": "project_bytes",
"type": "BYTES",
"mode": "NULLABLE"
},
{
"name": "lang",
"type": "STRING",
"mode": "NULLABLE"
}
]
This field array can then be copy/pasted (or further automated) in the fields editor when creating a new table using the UI.

Answer 3

I am not sure how it is possible using StandardSQL or Legacy SQL syntax. But you can get the schema in json format using command line.
From this link the command to do it would be:
bq show --schema --format=prettyjson [PROJECT_ID]:[DATASET].[TABLE] > [PATH_TO_FILE]