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Validate JSON fields ​

JSON imports can validate a row schema and, separately, typed paths inside a JSON document. Choose the contract that matches the stored value.

Row columns ​

Before INSERT FORMAT, create destination columns for the row fields. A JSON object field assigned to UInt64, for example, must convert to that declared integer range.

Typed document paths ​

Use JSON(path Type, ...) when one column stores an object with selected typed paths:

sql
CREATE TABLE typed_json
(
    doc JSON(user_id UInt64, details.price Decimal(18, 2))
);
INSERT INTO typed_json VALUES
    ('{"user_id":7,"details":{"price":"12.50"}}');
sql
SELECT doc.user_id, doc.details.price
FROM typed_json
FORMAT csv;
text
7,12.50

Missing and conflicting fields ​

A missing or explicit-null declared path uses its type default. Nullable paths remain NULL. An object path whose parent is a conflicting scalar is rejected; undeclared members remain in the document.

See JSON for type-hint declarations and JSON functions for extraction and transformations.