ODBCDriver2

Description

The ODBCDriver2 format is a binary, output-only format used to transfer query results over HTTP to the ClickHouse driver for ODBC. The driver requests it by setting default_format to ODBCDriver2; users normally don’t select it directly.

All integers in the stream are signed 32-bit values encoded in little-endian byte order. A string is encoded as its byte length followed by its bytes. The output has the following structure:

1. The value 2, indicating that two header rows follow.
2. A names header containing the value number_of_columns + 1, the string name, and each column name.
3. A types header containing the value number_of_columns + 1, the string type, and each ClickHouse data type name. LowCardinality wrappers are removed from these type names.
4. The data rows. Each row contains one text-serialized, length-prefixed value for every result column. Data rows don’t include their own row or column count, and the stream ends at EOF.

A NULL value is encoded with the length -1; an empty non-null string has length 0. Totals, when present, use the same row encoding and follow the ordinary rows.

Example usage

The following query is representative of the values covered by the format’s tests:

SELECT
    1 AS x,
    [2, 3] AS y,
    'Hello' AS z,
    NULL AS a
FORMAT ODBCDriver2

Because the result is binary, direct it to a file rather than a terminal:

clickhouse-client --query \
    "SELECT 1 AS x, [2, 3] AS y, 'Hello' AS z, NULL AS a FORMAT ODBCDriver2" \
    > result.bin

In normal use, the driver adds default_format=ODBCDriver2 to its HTTP requests and decodes the response.

Format settings

ODBCDriver2 uses the standard text-serialization settings for individual values. It has no settings specific to the format itself.