# GENERATE CHANGELOG DDL

## Syntax <a href="#synopsis" id="synopsis"></a>

{% code overflow="wrap" %}

```sql
GENERATE CHANGLEOG DDL changelog_name WITH(stream_parameter = value [, ...]);

GENERATE CHANGLEOG DDL changelog_name PRIMARY KEY(pk_name) WITH(stream_parameter = value [, ...]);
```

{% endcode %}

## Description

This command generates a CREATE DDL for CHANGELOG from a given schema or data — for example, [Data Store](/overview/core-concepts/store.md#entity) — that has corresponding [Data Formats (Serialization)](/reference/sql-syntax/data-format-serialization.md#protocol-buffers-and-descriptors). The command specially simplifies creating DDL for complex descriptors.

You can generate DDL if the current role has [`USAGE`](/overview/core-concepts/access-control.md#privilege) privileges on the [Data Store](/overview/core-concepts/store.md).

## Changelog Parameters <a href="#parameters" id="parameters"></a>

| Parameter Name                | Description                                                                                                                                                                                                                       |
| ----------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **`changelog_name`**          | The name of the new changelog.                                                                                                                                                                                                    |
| **`primary key`**             | <p>If you provide the primary key names they are added to the DDL. Otherwise, this is empty.<br></p><p><strong>Required?</strong> No.</p>                                                                                         |
| **`topic`**                   | <p>Name of the Kafka topic whose assigned data schema you're using (for Protobuf descriptor and Avro schema from SchemaRegistry).<br></p><p><strong>Required?</strong> Yes, for <code>AVRO</code>, <code>PROTOBUF</code></p>      |
| **`value.format`**            | <p>AVRO, PROTOBUF, JSON</p><p><strong>Required?</strong> Yes.</p>                                                                                                                                                                 |
| **`key.format`**              | <p><code>AVRO</code>, <code>PROTOBUF</code>, <code>JSON</code></p><p><strong>Required?</strong> No.</p>                                                                                                                           |
| **`data.json.value.content`** | <p>A string containing one or more JSON objects separated by commas. It serves as a data sample you use to infer the schema of the value field in Kafka.</p><p><strong>Required?</strong> Required only for <code>JSON</code></p> |
| **`data.json.key.content`**   | <p>A string containing one or more JSON objects separated by commas. It serves as a data sample you used to infer the schema of the key in Kafka.</p><p><strong>Required?</strong> Only for <code>JSON</code></p>                 |

## Generating "Create Changelog" DDL examples <a href="#examples" id="examples"></a>

**Generate a "create changelog" ddl for an entity in the current store, which includes a protobuf descriptor.**

{% code overflow="wrap" %}

```sql
GENERATE CHANGELOG DDL myChangelog with('topic'='pageviews_pb', 'value.format'='protobuf', 
'key.format'='protobuf');
```

{% endcode %}

The output would be:

{% code overflow="wrap" %}

```sql
CREATE CHANGELOG myChangelog(
 "viewtime" BIGINT NOT NULL,
  "userid" VARCHAR NOT NULL,
  "pageid" VARCHAR NOT NULL,
  PRIMARY KEY()  
 ) WITH ('key.format'='protobuf', 'key.type'='STRUCT<"userid" VARCHAR>', 'topic'='pageviews_pb', 'value.format'='protobuf');
```

{% endcode %}

**Generate a "create changelog" ddl for an entity in the current store, which includes AVRO in the Confluent Schema Registry.**

{% code overflow="wrap" %}

```sql
GENERATE CHANGELOG DDL myChangelog with('topic'='pageviews_avro', 'value.format'='avro', 
'key.format'='avro');
```

{% endcode %}

The output would be

{% code overflow="wrap" %}

```sql
CREATE CHANGELOG myChangelog(
 "viewtime" BIGINT ,
  "userid" VARCHAR ,
  "pageid" VARCHAR ,
  PRIMARY KEY() 
) WITH ('key.format'='avro', 'key.type'='STRUCT<"userid" VARCHAR>', 'topic'='pageviews_avro', 'value.format'='avro');     
```

{% endcode %}

**Generate a "create changelog" ddl for an entity whose content is JSON.**

{% code overflow="wrap" %}

```sql
GENERATE CHANGELOG DDL myChangelog with ('value.format'='json', 'data.json.value.content'='{"viewtime":1629453600000,"userid":"user_123","pageid":"page_1"},{"viewtime":1629457200000,"userid":"user_456","pageid":"page_2"},{"viewtime":1629460800000,"userid":"user_789","pageid":"page_3"}' );
```

{% endcode %}

The output would be

```sql
CREATE CHANGELOG myChangelog(
 "viewtime" BIGINT,
 "userid" VARCHAR,
 "pageid" VARCHAR,
  PRIMARY KEY() 
) WITH ('value.format'='json');
```


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