Create a table definition file for an external data source

This page describes how to create a table definition file for an external data source. An external data source is a data source that you can query directly even though the data is not stored in BigQuery.

A table definition file contains an external table's schema definition and metadata, such as the table's data format and related properties. When you create a table definition file, you can use schema auto-detection to define the schema for an external data source. You can provide the schema inline or you can provide a JSON file containing the schema definition.

Table definition files are used with the bq command-line tool. The properties in a table definition file also apply to creating an ExternalDataConfiguration when you use the REST API. You do not use table definition files when you create an external table by using the Google Cloud console.

You can create table definition files to describe a permanent or temporary external table for the following external data sources:

Cloud Storage
- Comma-separated values (CSV)
- Newline-delimited JSON
- Avro files
- Datastore export files
- ORC files
- Parquet files
- Firestore export files
Google Drive
- Comma-separated values (CSV)
- Newline-delimited JSON
- Avro files
- Google Sheets
Bigtable

Before you begin

To create a table definition file, you need the URI for your data source:

For a Drive data source, you need the Drive URI
For a Cloud Storage data source, you need the Cloud Storage URI
For a Bigtable data source, you need the Bigtable URI

Create a definition file for CSV, JSON, or Google Sheets files

Use one of the following methods to create a table definition file for CSV, JSON, or Google Sheets files in Cloud Storage or Drive:

Use the autodetect flag
Use an inline schema
Use a JSON schema file

Use the `autodetect` flag

If you specify a CSV, JSON, or Google Sheets file without including an inline schema description or a schema file, you can use the --autodetect flag to set the "autodetect" option to true in the table definition file. When auto-detect is enabled, BigQuery makes a best-effort attempt to automatically infer the schema. For more information, see Schema auto-detection for external data sources.

Use auto-detect with a Cloud Storage data source

Create a table definition file for a Cloud Storage data source:

Use the bq mkdef command with the --autodetect flag to create a table definition file. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
  --autodetect \
  --source_format=SOURCE_FORMAT \
  "URI" > /tmp/FILE_NAME
```
Replace the following:
- SOURCE_FORMAT: your file format
- FILE_NAME: the name of your table definition file
- URI: the Cloud Storage URI
  
  For example, gs://mybucket/myfile.

(Optional) Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in nano. The file should look like the following for a CSV external data source. Notice "autodetect" is set to true.

{
"autodetect": true,
"csvOptions": {
  "allowJaggedRows": false,
  "allowQuotedNewlines": false,
  "encoding": "UTF-8",
  "fieldDelimiter": ",",
  "quote": "\"",
  "skipLeadingRows": 0
},
"sourceFormat": "CSV",
"sourceUris": [
  "URI"
]
}

(Optional) Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to JSON source files, but there are settings that apply to CSV and Google Sheets files. For more information, see ExternalDataConfiguration in the API reference.

Use auto-detect with a Drive data source

Create a table definition file for a Drive data source:

Use the bq mkdef command with the --autodetect flag to create a table definition. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
   --autodetect \
   --source_format=SOURCE_FORMAT \
   "URI" > /tmp/FILE_NAME
```
Replace the following:
- SOURCE_FORMAT: your file format
- FILE_NAME: the name of your table definition file
- URI: the Drive URI
  
  For example, https://drive.google.com/open?id=123ABCD123AbcD123Abcd.
Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in nano. The file should look like the following for a Google Sheets external data source. Notice "autodetect" is set to true.
```
{
"autodetect": true,
"sourceFormat": "GOOGLE_SHEETS",
"sourceUris": [
  "URI"
]
}
```
(Optional) Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to JSON source files, but there are settings that apply to CSV and Google Sheets files. For more information, see ExternalDataConfiguration in the API reference.
To specify a particular sheet or a cell range in a Google Sheets file, add the range property to the table definition file. To query a particular sheet, specify the sheet name. To query a cell range, specify the range in the form: sheet_name!top_left_cell_id:bottom_right_cell_id, for example, "Sheet1!A1:B20". If the range parameter is not specified, the first sheet in the file is used.

Use an inline schema

If you do not want to use schema auto-detect, you can create a table definition file by providing an inline schema definition. To provide an inline schema definition, list the fields and data types on the command line in the following format: FIELD:DATA_TYPE,FIELD:DATA_TYPE.

Use an inline schema with a Cloud Storage or Drive data source

Create a table definition for a Cloud Storage or Drive data source by using an inline schema definition:

Use the bq mkdef command with the --noautodetect flag to create a table definition. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
  --noautodetect \
  --source_format=SOURCE_FORMAT \
  "URI" \
  FIELD:DATA_TYPE,FIELD:DATA_TYPE > /tmp/FILE_NAME
```
Replace the following
- SOURCE_FORMAT: the source file format
- URI: the Cloud Storage URI or your Drive URI
  
  For example, gs://mybucket/myfile for Cloud Storage or https://drive.google.com/open?id=123ABCD123AbcD123Abcd for Drive.
- FIELD:DATA_TYPE,FIELD:DATA_TYPE: the schema definition
  
  For example, Name:STRING,Address:STRING, ....
- FILE_NAME: the name of your table definition file

(Optional) Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in nano. The file should look like the following. Notice "autodetect" is not enabled, and the schema information is written to the table definition file.

{
"schema": {
  "fields": [
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    },
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    }
    ...
  ]
},
"sourceFormat": "NEWLINE_DELIMITED_JSON",
"sourceUris": [
  "URI"
]
}

(Optional) Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to JSON source files, but there are settings that apply to CSV and Google Sheets files. For more information, see ExternalDataConfiguration in the API reference.

Use a JSON schema file

If you do not want to use auto-detect or provide an inline schema definition, you can create a JSON schema file and reference it when creating your table definition file. Create the JSON schema file manually on your local machine. Referencing a JSON schema file stored in Cloud Storage or in Drive is not supported.

Use a schema file with a Cloud Storage data source

Create a table definition for a Cloud Storage data source using a JSON schema file:

Use the bq mkdef command with the --noautodetect flag to create a table definition. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
   --noautodetect \
   --source_format=SOURCE_FORMAT \
   "URI" \
  PATH_TO_SCHEMA_FILE > /tmp/FILE_NAME
```
Replace the following:
- SOURCE_FORMAT: your file format
- FILE_NAME: the name of your table definition file
- URI: the Cloud Storage URI
  
  For example, gs://mybucket/myfile.
- PATH_TO_SCHEMA_FILE: the location of the JSON schema file on your local machine

(Optional) Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in
nano. The file should look like the following. Notice "autodetect" is not enabled, and the schema information is written to the table definition file.

{
"schema": {
  "fields": [
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    },
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    }
    ...
  ]
},
"sourceFormat": "NEWLINE_DELIMITED_JSON",
"sourceUris": [
  "URI"
]
}

(Optional) Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to JSON source files, but there are settings that apply to CSV and Google Sheets files. For more information, see ExternalDataConfiguration in the API reference.

Use a schema file with a Drive data source

Create a table definition for a Drive data source using a JSON schema file:

Use the bq mkdef command with the --noautodetect flag to create a table definition. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
   --noautodetect \
   --source_format=source_format \
   "URI" \
   PATH_TO_SCHEMA_FILE > /tmp/FILE_NAME
```
Replace the following:
- SOURCE_FORMAT: the source file format
- URI: the Drive URI
  
  For example, https://drive.google.com/open?id=123ABCD123AbcD123Abcd.
- PATH_TO_SCHEMA_FILE: the location of the JSON schema file on your local machine
- FILE_NAME: the name of your table definition file

Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in nano. The file should look like the following. Notice "autodetect" is not enabled, and the schema information is written to the table definition file.

{
"schema": {
  "fields": [
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    },
    {
      "name": "FIELD",
      "type": "DATA_TYPE"
    }
    ...
  ]
},
"sourceFormat": "GOOGLE_SHEETS",
"sourceUris": [
  "URI"
]
}

(Optional) Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to JSON source files, but there are settings that apply to CSV and Google Sheets files. For more information, see ExternalDataConfiguration in the API reference.
To specify a particular sheet or a cell range in a Google Sheets file, add the range property to the table definition file. To query a particular sheet, specify the sheet name. To query a cell range, specify the range in the form: sheet_name!top_left_cell_id:bottom_right_cell_id, for example, "Sheet1!A1:B20". If the range parameter is not specified, the first sheet in the file is used.

Create a definition file for self-describing formats

Avro, Parquet, and ORC are self-describing formats. Data files in these formats contain their own schema information. If you use one of these formats as an external data source, then BigQuery automatically retrieves the schema using the source data. When creating a table definition, you don't need to use schema auto-detection, and you don't need to provide an inline schema definition or schema file.

You can create a table definition file for Avro, Parquet, or ORC data stored in Cloud Storage or Drive:

Use the bq mkdef command to create a table definition.
```
bq mkdef \
    --source_format=FORMAT \
    "URI" > FILE_NAME
```
Replace the following:
- FORMAT: the source format
- URI: the Cloud Storage URI or your Drive URI
  
  For example, gs://mybucket/myfile for Cloud Storage or https://drive.google.com/open?id=123ABCD123AbcD123Abcd for Drive.
- FILE_NAME: the name of your table definition file
Optional: Open the table definition file in a text editor. The file looks similar to the following:
```
{
   "sourceFormat": "AVRO",
   "sourceUris": [
   "URI"
    ]
}
```
Optional: Manually edit the table definition file to modify, add, or delete general settings such as maxBadRecords and ignoreUnknownValues. For more information, see ExternalDataConfiguration in the API reference.

Create a definition file for hive-partitioned data

Use the bq mkdef command with the hive_partitioning_mode and the hive_partitioning_source_uri_prefix flags to create a definition file for hive-partitioned data that's stored in Cloud Storage, Amazon Simple Storage Service (Amazon S3), or Azure Blob Storage.

Create a definition file for Datastore and Firestore

If you use a Datastore or Firestore export as an external data source, BigQuery automatically retrieves the schema using the self-describing source data. When creating a table definition, you don't need to provide an inline schema definition or schema file.

You can create a table definition file for Datastore and Firestore export data stored in Cloud Storage:

Use the bq mkdef command to create a table definition. You do not need to use the --noautodetect flag with Datastore or Firestore backup files. Schema auto-detect is disabled for these file types. The mkdef command generates a table definition file in JSON format. The following example creates a table definition and writes the output to a file: /tmp/file_name.
```
bq mkdef \
--source_format=DATASTORE_BACKUP \
"URI" > /tmp/FILE_NAME
```
Replace the following:
- URI: the Cloud Storage URI
- FILE_NAME: the name of your table definition file
The DATASTORE_BACKUP source format is used for both Datastore and Firestore.
(Optional) Open the table definition file in a text editor. For example, the command nano /tmp/file_name opens the file in nano. The file should look like the following. Notice there is no need for the "autodetect" setting.
```
{
"sourceFormat": "DATASTORE_BACKUP",
"sourceUris": [
  "gs://URI"
]
}
```
(Optional) Manually edit the table definition file to modify, add, or delete settings such as maxBadRecords and ignoreUnknownValues. There are no configuration settings that are specific to Datastore and Firestore export files. For more information, see ExternalDataConfiguration in the API reference.

Create a definition file for Bigtable

When you create a table definition file for Bigtable, you manually generate the file in JSON format. Using the mkdef command to create a table definition is not currently supported for Bigtable data sources. Schema auto-detect is also unsupported for Bigtable. For a list of Bigtable table definition options, see BigtableOptions in the REST API reference.

A JSON table definition file for Bigtable looks like the following. Using this table definition file, BigQuery reads data from a single column family, interpreting the values as binary encoded integers.

{
    "sourceFormat": "BIGTABLE",
    "sourceUris": [
        "https://googleapis.com/bigtable/projects/PROJECT_ID/instances/INSTANCE_ID/tables/TABLE_NAME"
    ],
    "bigtableOptions": {
        "columnFamilies" : [
            {
                "familyId": "FAMILY_ID",
                "type": "INTEGER",
                "encoding": "BINARY"
            }
        ]
    }
}

Replace the following:

PROJECT_ID: the project containing your Bigtable cluster
INSTANCE_ID: the Bigtable instance ID
TABLE_NAME: the name of the table you're querying
FAMILY_ID: the column family identifier

For more information, see Retrieving the Bigtable URI.

Wildcard support for table definition files

If your data is separated into multiple files, you can use an asterisk (*) wildcard to select multiple files. Use of the asterisk wildcard must follow these rules:

The asterisk can appear inside the object name or at the end of the object name.
Using multiple asterisks is unsupported. For example, the path gs://mybucket/fed-*/temp/*.csv is invalid.
Using an asterisk with the bucket name is unsupported.

Examples:

The following example shows how to select all of the files in all the folders which start with the prefix gs://mybucket/fed-samples/fed-sample:
```
gs://mybucket/fed-samples/fed-sample*
```
The following example shows how to select only files with a .csv extension in the folder named fed-samples and any subfolders of fed-samples:
```
gs://mybucket/fed-samples/*.csv
```
The following example shows how to select files with a naming pattern of fed-sample*.csv in the folder named fed-samples. This example doesn't select files in subfolders of fed-samples.
```
gs://mybucket/fed-samples/fed-sample*.csv
```

When using the bq command-line tool, you might need to escape the asterisk on some platforms.

If you use an asterisk wildcard, enclose the bucket and filename in quotes. For example, if you have two files named fed-sample000001.csv and fed-sample000002.csv and you want to use an asterisk to select both of them, the bucket URI would be "gs://mybucket/fed-sample*".

The * wildcard character is not allowed when creating table definition files for the following data sources:

Bigtable. For Bigtable data, only one data source can be specified. The URI value must be a valid HTTPS URL for a Bigtable table.
Datastore or Firestore. Datastore or Firestore exports stored in Cloud Storage. For Datastore backups, only one data source can be specified. The URI value must end with .backup_info or .export_metadata.
Drive. Data stored in Drive.

What's next

Learn how to query Cloud Storage data.
Learn how to query Drive data.
Learn how to query Bigtable data.