CREATE STREAM

Syntax

CREATE STREAM stream_name (
    column_name data_type [NOT NULL] [, ...]
) WITH (stream_parameter = value [, ...]);

Description

A stream is a sequence of immutable, partitioned, and partially-ordered events.

Note In DeltaStream, the terms events and records are synonymous.

A stream is a relational representation of data in a streaming Store, such as the data in a Kafka topic or a Kinesis stream. The records in a stream are independent of each other; this means there is no correlation between two records in a stream.

A stream declares the schema of the records, which includes the column name along with the column type and optional constraints. A stream is a type of Relation. Each relation belongs to a Schema in a Database, so the fully-qualified name of the relation would be <database>.<schema>.<relation>.

Arguments

stream_name

Specifies the name of the new stream. If the name is case sensitive you must wrap it in double quotes; otherwise the system uses the lower case name.

column_name

The name of a column to be created in the new stream. If the name is case sensitive you must wrap it in double quotes; otherwise the system uses the lower case name.

data_type

The data type of the column. This can include array specifiers. For more information on the data types supported by DeltaStream, see the Data Types reference.

NOT NULL

Defines a constraint on the column, ensuring it cannot contain NULL values.

WITH (stream_parameter = value [, …​ ])

Optionally, this clause specifies Stream Parameters.

Stream Parameters

Parameter Name	Description
topic	Name of the #entity that has the data for this stream. If the entity doesn't exist, an entity with this name is created in the corresponding store. Required: No Default value: Lowercase stream_name Type: String
store	Name of the store that hosts the #entity for this stream. Required: No Default value: Current session's store name Type: String Valid values: See LIST STORES.
value.format	Format of message value in the #entity. See Data Formats (Serialization) for more information regarding serialization formats. Required: Yes Type: String Valid values: JSON, AVRO, PROTOBUF, PRIMITIVE
timestamp	Name of the column in the stream to use as the timestamp. If not set, the timestamp of the message is used for time based operations such as window aggregations and joins. If the type of this timestamp field is BIGINT, it is expected that the values are epoch milliseconds UTC. Required: No Default value: Record's timestamp Type: String Valid values: Must be of type BIGINT or TIMESTAMP. See Data Types.
timestamp.format	The format to use for TIMESTAMP typed fields. See Data Types. Required: No Default value: sql Type: String Valid values: sql, iso8601

Kafka Specific Parameters

Parameters to be used if the associated Store is type KAFKA:

Parameter Name	Description
topic.partitions	The number of partitions to use when creating the entity, if applicable. If the topic already exist, then this value must be equal to the number of partitions in the existing Kafka entity. Required: Yes, unless topic already exists Default value: Leftmost source relation topic's partition count Type: Integer Valid values: [1, ...]
topic.replicas	The number of replicas to use when creating the topic, if applicable. If the topic already exists, then this value must be equal to the number of replicas in the existing Kafka entity. Required: Yes, unless topic already exists Default values: Leftmost source relation topic's replica count Type: Integer Valid values: [1, ...]
key.format	Format of message key in the #entity. This value can be the same as or different from the value.format. See Data Formats (Serialization) for more information regarding serialization formats. Required: No, unless key.type is set Default value: None Type: String Valid values: JSON, AVRO, PROTOBUF, PRIMITIVE
key.type	Declares the names and data types of key columns. The type is a STRUCT when key.format is a non-primitive value, e.g. 'key.type'='STRUCT<id BIGINT, name VARCHAR>'. For primitive values, the type is one of the Primitive Data Types, e.g. 'key.type'='VARCHAR'. Required: No, unless key.format is set Default value: None Type: String Valid values: See STRUCT in Data Types.
delivery.guarantee	The fault tolerance guarantees applied when producing to this stream. Required: No Default value: at_least_once Type: String Valid values: exactly_once: Produces to the stream using Kafka transactions. These transactions are committed when the query takes a checkpoint. On the consumer side, when setting the Kafka consumer isolation.level configuration to read_committed, only the committed records display. Since records aren't committed until the query takes a checkpoint, there is some additional delay when using this setting. at_least_once: Ensures that records are output to the stream at least once. During query checkpointing, the query waits to receive a confirmation of successful writes from the Kafka broker. If there are issues with the query then duplicate records are possible, as the query attempts to reprocess old data. none: There is no fault tolerance guarantee when producing to the stream. If there are issues on the Kafka broker then records may be lost; if there are issues with the query then output records may be duplicated.

Kinesis Specific Parameters

Parameters to be used if the associated Store is type KINESIS:

Parameter Name	Description
topic.shards	The number of shards to use when creating the topic, if applicable. If the topic already exists, then this value must be equal to the number of shards in the existing Kinesis stream. Required: Yes, unless topic already exists Default values: Leftmost source relation topic's shard count Type: Integer Valid values: [1, ...] Alias: kinesis.shards

Kinesis stores provide a delivery guarantee of at_least_once when producing events into a sink #entity.

Format-Specific Parameters

Avro

Parameters to be used when writing records into a stream if associated key.format or value.format is avro and the default Avro schema generation must be changed using a base schema for the key and/or value.

When generating an Avro schema for a column using a base schema:

• if the base schema has a field with the same name and data type as that of the column, then the field's definition from the base is used in the generated schema. This includes retaining the base schema's doc and logicalType for the field.

• if the base schema has a field with the same name as that of the column, but has a different data type, then an Avro schema type definition is generated from the column's data type with the field's doc taken from the its corresponding field in the base schema.

Notes

• Currently supported schema registries are Confluent Cloud and Confluent Platform.

• Known limitation: Confluent Schema Registry must use the default TopicNameStrategy for creating subject names. See CREATE SCHEMA_REGISTRY for more details.

Parameter Name	Description
avro.base.schema.store	Name of the store whose schema registry contains the Avro schema subject(s) to be used as the base schema for generating Avro schema for stream's key and/or value. Required: No Default values: Current session's store name Type: Identifier Valid values: See LIST STORES.
avro.base.subject.key	Name of the subject in the schema registry to obtain the base schema for generating Avro schema for stream's key. Required: No, unless key.format is set to avro and key.type is defined. Type: String
avro.base.subject.value	Name of the subject in the schema registry to obtain the base schema for generating Avro schema for stream's value columns. Required: No, unless value.format is set to avro . Type: String

Examples

Create a new stream with timestamp column and key/value formats

The following creates a new stream with name pageviews_json. This stream reads from an existing topic named pageviews in the default store demostore, and has a value.format of JSON. Additionally in the WITH clause, we specify that this stream has a key of type VARCHAR and uses the viewtime column as its timestamp:

demodb.public/demostore# LIST ENTITIES;
+------------------------------------------+------------+
|  Name                                    |  Is Leaf   |
+==========================================+============+
| pageviews                                | true       |
+------------------------------------------+------------+
demodb.public/demostore# CREATE STREAM pageviews_json (
   viewtime BIGINT,
   userid VARCHAR,
   pageid VARCHAR
) WITH (
   'topic'='pageviews',
   'value.format'='json',
   'key.format'='primitive',
   'key.type'='VARCHAR',
   'timestamp'='viewtime');
+------------+------------------------------+------------+------------------------------------------+
|  Type      |  Name                        |  Command   |  Summary                                 |
+============+==============================+============+==========================================+
| stream     | demodb.public.pageviews_json | CREATE     | stream "pageviews_json" was              |
|            |                              |            | successfully created                     |
+------------+------------------------------+------------+------------------------------------------+

Create a new stream in a specific store

The following creates a new stream pv_kinesis. This stream reads from an existing topic named pageviews in the store kinesis_store:

demodb.public/demostore# CREATE STREAM pv_kinesis (
   viewtime BIGINT,
   userid VARCHAR,
   pageid VARCHAR
) WITH ( 'topic'='pageviews', 'store'='kinesis_store', 'value.format'='json' );
+------------+--------------------------+------------+------------------------------------------+
|  Type      |  Name                    |  Command   |  Summary                                 |
+============+==========================+============+==========================================+
| stream     | demodb.public.pv_kinesis | CREATE     | stream "pv_kinesis" was successfully     |
|            |                          |            | created                                  |
+------------+--------------------------+------------+------------------------------------------+
demodb.public/demostore# LIST STREAMS;
+------------+------------+------------+------------+------------------------------------------+-------------------------------+-------------------------------+
|  Name      |  Type      |  Owner     |  State     |  Properties                              |  Created At                   |  Updated At                   |
+============+============+============+============+==========================================+===============================+===============================+
| pv_kinesis | stream     | sysadmin   | created    | { "value.format": "json", "topic":       | 2024-07-02 21:28:35 +0000 UTC | 2024-07-02 21:28:36 +0000 UTC |
|            |            |            |            | "pageviews", "store":                    |                               |                               |
|            |            |            |            | "kinesis_store" }                        |                               |                               |
+------------+------------+------------+------------+------------------------------------------+-------------------------------+-------------------------------+

Create a new stream without an existing entity

The following creates a new stream visit_count. As its corresponding topic doesn't exist in the store kinesis_store, it requires an additional topic parameter — for example, topic.shards — to create the new Kinesis data stream pv_count in the store:

demodb.public/kinesis_store# LIST ENTITIES;
+------------------------------------------+------------+
|  Name                                    |  Is Leaf   |
+==========================================+============+
| pageviews                                | true       |
+------------------------------------------+------------+                  

demodb.public/kinesis_store# CREATE STREAM visit_count (userid VARCHAR, pgcount BIGINT) WITH ('topic'='pv_count', 'value.format'='json', 'topic.shards' = 1);
+------------+---------------------------+------------+------------------------------------------+
|  Type      |  Name                     |  Command   |  Summary                                 |
+============+===========================+============+==========================================+
| stream     | demodb.public.visit_count | CREATE     | stream "visit_count" was successfully    |
|            |                           |            | created                                  |
+------------+---------------------------+------------+------------------------------------------+
demodb.public/kinesis_store# LIST ENTITIES;
+------------------------------------------+------------+
|  Name                                    |  Is Leaf   |
+==========================================+============+
| pageviews                                | true       |
| pv_count                                 | true       |
+------------------------------------------+------------+
  
demodb.public/kinesis_store# DESCRIBE ENTITY visit_count;
+------------------+------------+-------------+
|  Name            |  Shards    |  Descriptor |
+==================+============+=============+
| pageviews_one_kb | 1          | <null>      |
+------------------+------------+-------------+

demodb.public/kinesis_store# LIST STREAMS;
+-------------+------------+------------+------------+------------------------------------------+-------------------------------+-------------------------------+
|  Name       |  Type      |  Owner     |  State     |  Properties                              |  Created At                   |  Updated At                   |
+=============+============+============+============+==========================================+===============================+===============================+
| visit_count | stream     | sysadmin   | created    | { "topic.shards": 1, "value.format":     | 2024-07-02 21:32:20 +0000 UTC | 2024-07-02 21:32:32 +0000 UTC |
|             |            |            |            | "json", "topic": "pv_count", "store":    |                               |                               |
|             |            |            |            | "kinesis_iam_store" }                    |                               |                               |
+-------------+------------+------------+------------+------------------------------------------+-------------------------------+-------------------------------+

Create a new stream for an existing entity

The following creates a new users stream for the existing users #entity in the current Store. This DDL implies that the name of the stream should be used as the name of the entity that hosts the records. This DDL also implies the original structure for the users entity:

CREATE STREAM "users" (
    registertime BIGINT,
    userid VARCHAR,
    regionid VARCHAR,
    gender VARCHAR,
    interests ARRAY<VARCHAR>,
    contactinfo STRUCT<
        phone VARCHAR,
        city VARCHAR,
        "state" VARCHAR,
        zipcode VARCHAR>
) WITH ( 'value.format'='json' );

Create a new stream with case-sensitive columns

The following creates a new stream CaseSensitivePV in the database DataBase and schema Schema2. This stream reads from a topic named case_sensitive_pageviews in store OtherStore and has a value.format of AVRO and key.format of PROTOBUF. As the key.format is included, key.type must be provided and the value in this example is STRUCT<pageid VARCHAR>.

Note that many of the columns are in quotes, indicating they are case-sensitive. The case insensitive column named CaseInsensitiveCol is lowercase as caseinsensitivecol when the relation is created. In the parameters, the timestamp for this relation is also specified; queries processing data using this relation as the source refer to the timestamp column ViewTime as the event's timestamp.

CREATE STREAM "DataBase"."Schema2"."CaseSensitivePV" (
   "ViewTime" BIGINT,
   "userID" VARCHAR,
   "PageId" VARCHAR,
   "CaseSensitiveCol" BIGINT,
   CaseInsensitiveCol BIGINT
)
WITH (
   'topic'='case_sensitive_pageviews',
   'store'='OtherStore',
   'value.format'='avro',
   'key.format'='protobuf',
   'key.type'='STRUCT<pageid VARCHAR>',
   'timestamp'='ViewTime'
);

Create a new stream with `NOT NULL` column

The following creates a new stream, users. Two columns in this stream are defined with the NOT NULL constraint:

1. registertime

2. contactinfo

This means in any valid record from this stream, these two columns are not allowed to contain null values.

CREATE STREAM "users" (
    registertime BIGINT NOT NULL,
    userid VARCHAR, 
    interests ARRAY<VARCHAR>,
    contactinfo STRUCT<phone VARCHAR, city VARCHAR, "state" VARCHAR, zipcode VARCHAR> NOT NULL
)
WITH (
   'topic'='users', 
    'key.format'='json', 
    'key.type'='STRUCT<userid VARCHAR>', 
    'value.format'='json'
);

Create a new stream with format-specific properties for Avro

The following creates a new stream, usersInfo,. The key and value of the records in this stream are in avro format. The stream uses subjects from a store called sr_store as the base Avro schema to generate Avro schema for usersInfo's key and value. users_data-key subject is used to generate the key's Avro schema; the users_data-value subject is used to generate the value's Avro schema for the records written into usersInfo.

CREATE STREAM "usersInfo" (
    registertime BIGINT NOT NULL,
    userid VARCHAR, 
    interests ARRAY<VARCHAR>,
    contactinfo STRUCT<phone VARCHAR, city VARCHAR, "state" VARCHAR, zipcode VARCHAR> NOT NULL
)
WITH (
    'topic'='usersInfo', 
    'key.format'='avro',
    'key.type'='STRUCT<userid VARCHAR>', 
    'value.format'='avro',
    'avro.base.store.name' = sr_store,
    'avro.base.subject.key' = 'users_data-key',
    'avro.base.subject.value' = 'users_data-value'
);