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JSON Format Settings

The JSON extension can attempt to determine the format of a JSON file when setting format to auto. Here are some example JSON files and the corresponding format settings that should be used.

In each of the below cases, the format setting was not needed, as DuckDB was able to infer it correctly, but it is included for illustrative purposes. A query of this shape would work in each case:

SELECT *
FROM filename.json;

Format: newline_delimited

With format = 'newline_delimited' newline-delimited JSON can be parsed. Each line is a JSON.

We use the example file records.json with the following content:

{"key1":"value1", "key2": "value1"}
{"key1":"value2", "key2": "value2"}
{"key1":"value3", "key2": "value3"}

SELECT *
FROM read_json('records.json', format = 'newline_delimited');
key1 key2
value1 value1
value2 value2
value3 value3

Format: array

If the JSON file contains a JSON array of objects (pretty-printed or not), array_of_objects may be used. To demonstrate its use, we use the example file records-in-array.json:

[
    {"key1":"value1", "key2": "value1"},
    {"key1":"value2", "key2": "value2"},
    {"key1":"value3", "key2": "value3"}
]

SELECT *
FROM read_json('records-in-array.json', format = 'array');
key1 key2
value1 value1
value2 value2
value3 value3

Format: unstructured

If the JSON file contains JSON that is not newline-delimited or an array, unstructured may be used. To demonstrate its use, we use the example file unstructured.json:

{
    "key1":"value1",
    "key2":"value1"
}
{
    "key1":"value2",
    "key2":"value2"
}
{
    "key1":"value3",
    "key2":"value3"
}

SELECT *
FROM read_json('unstructured.json', format = 'unstructured');
key1 key2
value1 value1
value2 value2
value3 value3

Records Settings

The JSON extension can attempt to determine whether a JSON file contains records when setting records = auto. When records = true, the JSON extension expects JSON objects, and will unpack the fields of JSON objects into individual columns.

Continuing with the same example file, records.json:

{"key1":"value1", "key2": "value1"}
{"key1":"value2", "key2": "value2"}
{"key1":"value3", "key2": "value3"}

SELECT *
FROM read_json('records.json', records = true);
key1 key2
value1 value1
value2 value2
value3 value3

When records = false, the JSON extension will not unpack the top-level objects, and create STRUCTs instead:

SELECT *
FROM read_json('records.json', records = false);
json
{'key1': value1, 'key2': value1}
{'key1': value2, 'key2': value2}
{'key1': value3, 'key2': value3}

This is especially useful if we have non-object JSON, for example, arrays.json:

[1, 2, 3]
[4, 5, 6]
[7, 8, 9]

SELECT *
FROM read_json('arrays.json', records = false);
json
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
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