ekuiper-new/docs/sqls/streams.md

Stream specs

Data types

In XStream, each column or an expression has a related data type. A data type describes (and constrains) the set of values that a column of that type can hold or an expression of that type can produce.

Below is the list of data types supported.

#	Data type	Description
1	bigint
2	float
3	string
4	datetime	Not support.
5	boolean
6	array	The array type, can be any simple types or struct type (#1 - #5, and #7).
7	struct	The complex type.

Language definitions

CREATE STREAM   
    stream_name   
    ( column_name <data_type> [ ,...n ] )
    WITH ( property_name = expression [, ...] );

The supported property names.

Property name	Optional	Description
DATASOURCE	false	The topic names list if it's a MQTT data source.
FORMAT	false	JSON.
KEY	true	Reserved key, currently the field is not used. It will be used for GROUP BY statements.
TYPE	false	The data format, currently the value can only be "JSON".
StrictValidation	false	To control validation behavior of message field against stream schema. See StrictValidation for more info.
CONF_KEY	false	If additional configuration items are requied to be configured, then specify the config key here. See MQTT stream for more info.

Example 1,

my_stream 
  (id bigint, name string, score float)
WITH ( datasource = "topic/temperature", FORMAT = "json", KEY = "id");

The stream will subscribe to MQTT topic topic/temperature, the server connection uses servers key of default section in configuration file $xstream/etc/mqtt_source.yaml.

• See MQTT source for more info.

Example 2,

demo (
		USERID BIGINT,
		FIRST_NAME STRING,
		LAST_NAME STRING,
		NICKNAMES ARRAY(STRING),
		Gender BOOLEAN,
		ADDRESS STRUCT(STREET_NAME STRING, NUMBER BIGINT),
	) WITH (datasource="test/", FORMAT="JSON", KEY="USERID", CONF_KEY="demo");

The stream will subscribe to MQTT topic test/, the server connection uses settings of demo section in configuration file $xstream/etc/mqtt_source.yaml.

• See MQTT source for more info.

• See rules and streams CLI docs for more information of rules & streams management.

StrictValidation

The value of StrictValidation can be true or false.
1) True: Drop the message if the message  is not satisfy with the stream definition.
2) False: Keep the message, but fill the missing field with default empty value.

bigint: 0
float: 0.0
string: ""
datetime: (NOT support yet)
boolean: false
array: zero length array
struct: null value

See Query languange element for more inforamtion of SQL language.