JSON

Documentation for the JSON format

Input	Output	Alias
✔	✔

Description

The JSON format reads and outputs data in the JSON format.

The JSON format returns the following:

Parameter	Description
meta	Column names and types.
data	Data tables
rows	The total number of output rows.
rows_before_limit_at_least	The lower estimate of the number of rows there would have been without LIMIT. Output only if the query contains LIMIT. This estimate is calculated from the blocks of data processed in the query pipeline before the limit transform, but could then be discarded by the limit transform. If the blocks didn’t even reach the limit transform in the query pipeline, they don’t participate in the estimation.
statistics	Statistics such as elapsed, rows_read, bytes_read.
totals	Total values (when using WITH TOTALS).
extremes	Extreme values (when extremes are set to 1).

The JSON type is compatible with JavaScript. To ensure this, some characters are additionally escaped:

• the slash / is escaped as \/
• alternative line breaks U+2028 and U+2029, which break some browsers, are escaped as \uXXXX.
• ASCII control characters are escaped: backspace, form feed, line feed, carriage return, and horizontal tab are replaced with \b, \f, \n, \r, \t , as well as the remaining bytes in the 00-1F range using \uXXXX sequences.
• Invalid UTF-8 sequences are changed to the replacement character � so the output text will consist of valid UTF-8 sequences.

For compatibility with JavaScript, Int64 and UInt64 integers are enclosed in double quotes by default. To remove the quotes, you can set the configuration parameter output_format_json_quote_64bit_integers to 0.

ClickHouse supports NULL, which is displayed as null in the JSON output. To enable +nan, -nan, +inf, -inf values in output, set the output_format_json_quote_denormals to 1.

Example usage

Example:

SELECT SearchPhrase, count() AS c FROM test.hits GROUP BY SearchPhrase WITH TOTALS ORDER BY c DESC LIMIT 5 FORMAT JSON

{
        "meta":
        [
                {
                        "name": "num",
                        "type": "Int32"
                },
                {
                        "name": "str",
                        "type": "String"
                },
                {
                        "name": "arr",
                        "type": "Array(UInt8)"
                }
        ],

        "data":
        [
                {
                        "num": 42,
                        "str": "hello",
                        "arr": [0,1]
                },
                {
                        "num": 43,
                        "str": "hello",
                        "arr": [0,1,2]
                },
                {
                        "num": 44,
                        "str": "hello",
                        "arr": [0,1,2,3]
                }
        ],

        "rows": 3,

        "rows_before_limit_at_least": 3,

        "statistics":
        {
                "elapsed": 0.001137687,
                "rows_read": 3,
                "bytes_read": 24
        }
}

Format settings

For JSON input format, if setting input_format_json_validate_types_from_metadata is set to 1, the types from metadata in input data will be compared with the types of the corresponding columns from the table.

See also

• JSONEachRow format
• output_format_json_array_of_rows setting