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Trigger

Triggers allow events to be periodically generated. Trigger definition can be used to define a trigger. A trigger also works like a stream with a predefined schema.

Purpose

For some use cases the system should be able to periodically generate events based on a specified time interval to perform some periodic executions.

A trigger can be performed for a 'start' operation, for a given <time interval>, or for a given '<cron expression>'.

Syntax

The syntax for a trigger definition is as follows.

CREATE TRIGGER <trigger name> at ('start'| every <time interval>| '<cron expression>');

Similar to streams, triggers can be used as inputs. They adhere to the following stream definition and produce the triggered_time attribute of the long type.

CREATE STREAM <trigger name> (triggered_time long);

The following types of triggeres are currently supported:

Trigger typeDescription
'start'An event is triggered when Stream is started.
every <time interval>An event is triggered periodically at the given time interval.
'<cron expression>'An event is triggered periodically based on the given cron expression. For configuration details, see quartz-scheduler.

Examples

  • Triggering events regularly at specific time intervals

    The following query triggers events every 5 minutes.

    CREATE TRIGGER FiveMinTriggerStream WITH(interval= 5 min);

  • Triggering events at a specific time on specified days

    The following query triggers an event at 10.15 AM on every weekdays.

    CREATE TRIGGER FiveMinTriggerStream1 WITH (expression='0 15 10 ? * MON-FRI');