Function registerDataTypeJSON

src/DataTypes/DataTypeObject.cpp:864–2200

}

void registerDataTypeJSON(DataTypeFactory & factory)
{
    factory.registerDataType("JSON", createJSON, DataTypeFactory::Case::Insensitive, Documentation{
            .description = String(R"DOCS_MD(
:::tip
Check out our [JSON best practice guide](/docs/best-practices/use-json-where-appropriate) for examples, advanced features and considerations for using the JSON type.
:::

The `JSON` type stores JavaScript Object Notation (JSON) documents in a single column.

:::note
In ClickHouse Open-Source JSON data type is marked as production ready in version 25.3. It's not recommended to use this type in production in previous versions.
:::

To declare a column of `JSON` type, you can use the following syntax:

```sql
<column_name> JSON
(
    max_dynamic_paths=N,
    max_dynamic_types=M,
    some.path TypeName,
    SKIP path.to.skip,
    SKIP REGEXP 'paths_regexp'
)
```
Where the parameters in the syntax above are defined as:

| Parameter                   | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | Default Value |
|-----------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|
| `max_dynamic_paths`         | An optional parameter indicating how many paths can be stored separately as sub-columns across single block of data that is stored separately (for example across single data part for MergeTree table). <br/><br/>If this limit is exceeded, all other paths will be stored together in a single structure called [shared data](#shared-data-structure).<br/><br/>There are also [ways](#controlling-the-number-of-dynamic-paths) how to change the limit on dynamic paths without changing this parameter. | `1024`        |
| `max_dynamic_types`         | An optional parameter between `1` and `255` indicating how many different data types can be stored separately inside a single path column with type `Dynamic` across single block of data that is stored separately (for example across single data part for MergeTree table). <br/><br/>If this limit is exceeded, all new types will be stored together in a single structure called `shared variant`.                                                                                    | `32`          |
| `some.path TypeName`        | An optional type hint for particular path in the JSON. Such paths will be always stored as sub-columns with specified type.                                                                                                                                                                                                                                                                                                                                                                                  |               |
| `SKIP path.to.skip`         | An optional hint for particular path that should be skipped during JSON parsing. Such paths will never be stored in the JSON column. If specified path is a nested JSON object, the whole nested object will be skipped.                                                                                                                                                                                                                                                                                     |               |
| `SKIP REGEXP 'path_regexp'` | An optional hint with a regular expression that is used to skip paths during JSON parsing. All paths that match this regular expression will never be stored in the JSON column.                                                                                                                                                                                                                                                                                                                             |               |

## Creating `JSON` {#creating-json}

In this section we'll take a look at the various ways that you can create `JSON`.

### Using `JSON` in a table column definition {#using-json-in-a-table-column-definition}

```sql title="Query (Example 1)"
CREATE TABLE test (json JSON) ENGINE = Memory;
INSERT INTO test VALUES ('{"a" : {"b" : 42}, "c" : [1, 2, 3]}'), ('{"f" : "Hello, World!"}'), ('{"a" : {"b" : 43, "e" : 10}, "c" : [4, 5, 6]}');
SELECT json FROM test;
```

```text title="Response (Example 1)"
┌─json────────────────────────────────────────┐
│ {"a":{"b":"42"},"c":["1","2","3"]}          │
│ {"f":"Hello, World!"}                       │
│ {"a":{"b":"43","e":"10"},"c":["4","5","6"]} │
└─────────────────────────────────────────────┘
```

```sql title="Query (Example 2)"
CREATE TABLE test (json JSON(a.b UInt32, SKIP a.e)) ENGINE = Memory;