This is an example of how to use the READ_NOS table operator with a return type of NOSREAD_KEYS to list external files at a specified location.
List of Files at a Location
This statement performs a query of a JSON file using the READ_NOS_json_fm function mapping. The files specified by the LOCATION option include the extensions, .json and .json.gz. If the files have extension other than .json, .json.gz, .csv, or .tsv, you must specify an ON clause where the payload of the input table must match the payload returned by READ_NOS.
Create the function mapping READ_NOS_json_fm, if not already created. See Example: Function Mapping Definition Using EXTERNAL SECURITY Clause for JSON Data Files.
Perform the READ_NOS:
SELECT location
FROM READ_NOS_json_fm (
USING
LOCATION ('/S3/td-usgs.s3.amazonaws.com/JSONDATA')
RETURNTYPE('NOSREAD_KEYS')
) AS d;
Your results will be similar to the following:
Location -------------------------------------------------------------- /S3/td-usgs.s3.amazonaws.com/JSONDATA/09424900/2018/07/03.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09424900/2018/06/29.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09429070/2018/06/29.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09400815/2018/07/21.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09400568/2018/07/02.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09424900/2018/06/28.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09400815/2018/07/24.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09423560/2018/07/11.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09400815/2018/06/27.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09474000/2018/07/12.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09429070/2018/06/28.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09380000/2018/06/28.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09474000/2018/07/11.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09424900/2018/07/23.json /S3/td-usgs.s3.amazonaws.com/JSONDATA/09423560/2018/07/26.json