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JSON Extract example

A short example on how to extract base types from JSON

JSON Extract example​

This is just a short example that illustrates the use of JSONExtract functions.

Create a table:

CREATE TABLE default.json_extract_example
(
    `rawJSON` String EPHEMERAL,
    `a1` String DEFAULT JSONExtractString(rawJSON, 'a1'),
    `a2` Boolean DEFAULT JSONExtractBool(rawJSON, 'a2'),
    `a3.aa1` Float DEFAULT JSONExtractFloat(JSONExtractRaw(rawJSON, 'a3'), 'aa1'),
    `a3.aa2` UInt8 DEFAULT JSONExtractUInt(JSONExtractRaw(rawJSON, 'a3'), 'aa2')
)
ENGINE = MergeTree
ORDER BY (a1, a2)

Add your JSON raw string:

INSERT INTO default.json_extract_example (rawJSON) VALUES ('{"a1": "XX", "a2": true, "a3":{"aa1":23.11,"aa2":12}}');

Query your data:

SELECT *
FROM json_extract_example
FORMAT Pretty

Yields:

┏━━━━┳━━━━━━┳━━━━━━━━┳━━━━━━━━┓
┃ a1 ┃ a2   ┃ a3.aa1 ┃ a3.aa2 ┃
┡━━━━╇━━━━━━╇━━━━━━━━╇━━━━━━━━┩
│ XX │ true │  23.11 │     12 │
└────┴──────┴────────┴────────┘

Each stored as the original JSON type:

SELECT
    toTypeName(a1),
    toTypeName(a2),
    toTypeName(a3.aa1),
    toTypeName(a3.aa2)
FROM default.json_extract_example
FORMAT Pretty

┏━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━┓
┃ toTypeName(a1) ┃ toTypeName(a2) ┃ toTypeName(a3.aa1) ┃ toTypeName(a3.aa2) ┃
┡━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━━━━━━━━━┩
│ String         │ Bool           │ Float32            │ UInt8              │
└────────────────┴────────────────┴────────────────────┴────────────────────┘
· One min read