ClickHouse/docs/en/sql-reference/table-functions/gcs.md

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gcs Table Function

Provides a table-like interface to SELECT and INSERT data from Google Cloud Storage. Requires the Storage Object User IAM role.

This is an alias of the s3 table function.

If you have multiple replicas in your cluster, you can use the s3Cluster function (which works with GCS) instead to parallelize inserts.

Syntax

gcs(path [,hmac_key, hmac_secret] [,format] [,structure] [,compression])

:::tip GCS The GCS Table Function integrates with Google Cloud Storage by using the GCS XML API and HMAC keys. See the Google interoperability docs for more details about the endpoint and HMAC.

:::

Arguments

• path — Bucket url with path to file. Supports following wildcards in readonly mode: *, **, ?, {abc,def} and {N..M} where N, M — numbers, 'abc', 'def' — strings.

:::note GCS The GCS path is in this format as the endpoint for the Google XML API is different than the JSON API:

https://storage.googleapis.com/<bucket>/<folder>/<filename(s)>

and not https://storage.cloud.google.com. :::

• format — The format of the file.
• structure — Structure of the table. Format 'column1_name column1_type, column2_name column2_type, ...'.
• compression — Parameter is optional. Supported values: none, gzip/gz, brotli/br, xz/LZMA, zstd/zst. By default, it will autodetect compression by file extension.

Returned value

A table with the specified structure for reading or writing data in the specified file.

Examples

Selecting the first two rows from the table from GCS file https://storage.googleapis.com/my-test-bucket-768/data.csv:

SELECT *
FROM gcs('https://storage.googleapis.com/my-test-bucket-768/data.csv', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32')
LIMIT 2;

┌─column1─┬─column2─┬─column3─┐
│       1 │       2 │       3 │
│       3 │       2 │       1 │
└─────────┴─────────┴─────────┘

The similar but from file with gzip compression:

SELECT *
FROM gcs('https://storage.googleapis.com/my-test-bucket-768/data.csv.gz', 'CSV', 'column1 UInt32, column2 UInt32, column3 UInt32', 'gzip')
LIMIT 2;

┌─column1─┬─column2─┬─column3─┐
│       1 │       2 │       3 │
│       3 │       2 │       1 │
└─────────┴─────────┴─────────┘

Usage

Suppose that we have several files with following URIs on GCS:

• 'https://storage.googleapis.com/my-test-bucket-768/some_prefix/some_file_1.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/some_prefix/some_file_2.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/some_prefix/some_file_3.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/some_prefix/some_file_4.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/another_prefix/some_file_1.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/another_prefix/some_file_2.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/another_prefix/some_file_3.csv'
• 'https://storage.googleapis.com/my-test-bucket-768/another_prefix/some_file_4.csv'

Count the amount of rows in files ending with numbers from 1 to 3:

SELECT count(*)
FROM gcs('https://storage.googleapis.com/my-test-bucket-768/{some,another}_prefix/some_file_{1..3}.csv', 'CSV', 'name String, value UInt32')

┌─count()─┐
│      18 │
└─────────┘

Count the total amount of rows in all files in these two directories:

SELECT count(*)
FROM gcs('https://storage.googleapis.com/my-test-bucket-768/{some,another}_prefix/*', 'CSV', 'name String, value UInt32')

┌─count()─┐
│      24 │
└─────────┘

:::warning If your listing of files contains number ranges with leading zeros, use the construction with braces for each digit separately or use ?. :::

Count the total amount of rows in files named file-000.csv, file-001.csv, … , file-999.csv:

SELECT count(*)
FROM gcs('https://storage.googleapis.com/my-test-bucket-768/big_prefix/file-{000..999}.csv', 'CSV', 'name String, value UInt32');

┌─count()─┐
│      12 │
└─────────┘

Insert data into file test-data.csv.gz:

INSERT INTO FUNCTION gcs('https://storage.googleapis.com/my-test-bucket-768/test-data.csv.gz', 'CSV', 'name String, value UInt32', 'gzip')
VALUES ('test-data', 1), ('test-data-2', 2);

Insert data into file test-data.csv.gz from existing table:

INSERT INTO FUNCTION gcs('https://storage.googleapis.com/my-test-bucket-768/test-data.csv.gz', 'CSV', 'name String, value UInt32', 'gzip')
SELECT name, value FROM existing_table;

Glob ** can be used for recursive directory traversal. Consider the below example, it will fetch all files from my-test-bucket-768 directory recursively:

SELECT * FROM gcs('https://storage.googleapis.com/my-test-bucket-768/**', 'CSV', 'name String, value UInt32', 'gzip');

The below get data from all test-data.csv.gz files from any folder inside my-test-bucket directory recursively:

SELECT * FROM gcs('https://storage.googleapis.com/my-test-bucket-768/**/test-data.csv.gz', 'CSV', 'name String, value UInt32', 'gzip');

Partitioned Write

If you specify PARTITION BY expression when inserting data into GCS table, a separate file is created for each partition value. Splitting the data into separate files helps to improve reading operations efficiency.

Examples

1. Using partition ID in a key creates separate files:

INSERT INTO TABLE FUNCTION
    gcs('http://bucket.amazonaws.com/my_bucket/file_{_partition_id}.csv', 'CSV', 'a String, b UInt32, c UInt32')
    PARTITION BY a VALUES ('x', 2, 3), ('x', 4, 5), ('y', 11, 12), ('y', 13, 14), ('z', 21, 22), ('z', 23, 24);

As a result, the data is written into three files: file_x.csv, file_y.csv, and file_z.csv.

2. Using partition ID in a bucket name creates files in different buckets:

INSERT INTO TABLE FUNCTION
    gcs('http://bucket.amazonaws.com/my_bucket_{_partition_id}/file.csv', 'CSV', 'a UInt32, b UInt32, c UInt32')
    PARTITION BY a VALUES (1, 2, 3), (1, 4, 5), (10, 11, 12), (10, 13, 14), (20, 21, 22), (20, 23, 24);

As a result, the data is written into three files in different buckets: my_bucket_1/file.csv, my_bucket_10/file.csv, and my_bucket_20/file.csv.

See Also

• S3 table function
• S3 engine