Managing Stored Data via Streams

This section covers how to manage stored data in event tables via streams.

Inserting records

Prerequisites

In order to insert events to a table:

• General prerequisites should be completed.
• The event stream from which the events to be inserted are taken should be defined.
• The table to which events are to be inserted should be defined. For more information, see Defining a table.

Query syntax

The following is the syntax to insert events into a table.

from <STREAM_NAME>
select <ATTRIBUTE1_NAME>, <ATTRIBUTE2_NAME>, <ATTRIBUTE3_NAME> ...
insert into <TABLE_NAME>;

Example

The following query inserts events from the FooStream stream to the FooTable table with the symbol, price, and volume attributes.

from FooStream
select symbol, price, volume
insert into FooTable;

Retrieving records

Prerequisites

In order to retrieve events from a table:

• General prerequisites should be completed.
• The table to be read should be already defined. For more information, see Defining a table.
• One or more events should be inserted into the table. For more information, see Inserting events.

Query syntax

The following is the query syntax to retrieve events from an existing table. For more information, please refer to Siddhi Query Guide - Join Table.

from <STREAM_NAME> join <TABLE_NAME>
    on <CONDITION>
select (<STREAM_NAME>|<TABLE_NAME>).<ATTRIBUTE1_NAME>, (<STREAM_NAME>|<TABLE_NAME>).<ATTRIBUTE2_NAME>, ...
insert into <OUTPUT_STREAM>

Example

The following query joins the FooStream events with the events stored in the StockTable table. An output event is created for each matching pair of events, and it is inserted into another stream named OutputStream. 

from FooStream#window.length(1) join StockTable
select FooStream.symbol as checkSymbol, StockTable.symbol as symbol, StockTable.volume as volume 
insert into OutputStream

The information inserted with the output event is as follows.

Updating a table

This section explains how to update the selected records of an existing table.

Prerequisites

In order to update events in a table:

• General prerequisites should be completed.
• The table to be updated should be already defined. For more information, see Defining a table.
• The event stream with the events based on which the updates are made must be already defined.
• One or more events should be inserted into the table. For more information, see Inserting events.

Query syntax

from <STREAM_NAME> 
select <ATTRIBUTE1_NAME>, <ATTRIBUTE2_NAME>, ...
update <TABLE_NAME> (for <OUTPUT_EVENT_TYPE>)? 
    set <TABLE_NAME>.<ATTRIBUTE_NAME> = (<ATTRIBUTE_NAME>|<EXPRESSION>)?, <TABLE_NAME>.<ATTRIBUTE_NAME> = (<ATTRIBUTE_NAME>|<EXPRESSION>)?, ...
    on <CONDITION>

Example

The following query updates the events in the FooTable table with values from the latest events of the FooStream event stream. The events in the table are updated only if the existing record in the table has the same value as the new event for the symbol attribute, and a value greater than 50 for the price attribute. 

from FooStream
select symbol, price, volume
update FooTable 
set FooTable.symbol = symbol, FooTable.price = price, FooTable.volume = volume 
on (FooTable.symbol == symbol and price > 50)

Methods of Updating the columns in a table

This section gives further information on methods of updating the columns in an existing table.

The value used for updating a table column can be any of the following:

• A constant

  FROM sensorStream
  SELECT sensorId, temperature, humidity
  UPDATE sensorTable
      SET sensorTable.column_temp = 1 
      ON  sensorId < sensorTable.column_ID

• One of the attributes specified in the SELECT clause

  FROM fooStream
  SELECT roomNo, time: timestampInMilliseconds() as ts
  UPDATE barTable
      SET barTable.timestamp = ts
      ON  barTable.room_no == roomNo AND roomNo > 2

• A basic arithmetic operation applied on an output attribute

  FROM sensorStream
  SELECT sensorId, temperature, humidity
  UPDATE sensorTable
      SET sensorTable.column_temp = temperature + 10  
      ON  sensorId < sensorTable.column_ID

• A basic arithmetic operation applied to a column value in the event table

  FROM sensorStream
  SELECT sensorId, temperature, humidity
  UPDATE sensorTable
      SET sensorTable.column_temp = sensorTable.column_temp + 10  
      ON  sensorId < sensorTable.column_ID

Deleting Records

This section explains how to delete existing records in a table based on a specific condition.

Prerequisites

In order to delete selected events in a table:

• General prerequisites should be completed.
• The table with the records to be deleted should be already defined. For more information, see Defining a table.
• The event stream with the events with which the records in the table are compared (i.e., to apply the condition based on which the events are deleted) must be already defined.
• One or more events should be inserted into the table. For more information, see Inserting events.

Query syntax

from <STREAM_NAME> 
select <ATTRIBUTE1_NAME>, <ATTRIBUTE2_NAME>, ...
delete <TABLE_NAME> (for <OUTPUT_EVENT_TYPE>)?
    on <CONDITION>

Example

This query deletes the events in the RoomTypeTable table if its value for the roomNo attribute is equal to the roomNumber attribute value of DeleteStream.

from DeleteStream
delete RoomTypeTable
    on RoomTypeTable.roomNo == roomNumber;

Searching records

This section explains how to check whether a specific record exists in an event table.

Prerequisites

In order to search for a record in a table that matches a specific condition:

• General prerequisites should be completed.
• The table to be searched should be already defined. For more information, see Defining a table.
• The event stream with the events with which the records in the table are compared (i.e., to apply the condition based on which the events are searched) must be already defined.
• One or more events should be inserted into the table. For more information, see Inserting events.

Query syntax

from <STREAM_NAME>[<CONDITION> in <TABLE_NAME>]
select <ATTRIBUTE1_NAME>, <ATTRIBUTE2_NAME>, ...
insert into <OUTPUT_STREAM_NAME>

Example

The following query matches events arriving from the FooStream event stream with the existing recored stored in the StockTable table. If the symbol attribute of an event saved in the table has the same value as the event from the FooStream stream, that event is inserted into the OutputStream stream.

from FooStream[StockTable.symbol==symbol in StockTable]
insert into OutputStream;

Inserting/updating records

This section explains how to update a selection of records in a table based on the new events from a specific event stream. The selection is made based on a specific condition that matches events from the stream with events in the table. When the events from the stream have no matching events in the table, they are inserted into the table as new events.

Prerequisites

• General prerequisites should be completed.
• The table for which this operations is to be performed must be already defined. For more information, see Defining a table.
• The event stream from which the events with which the records in the table are compared (i.e., to apply the condition based on which the events are inserted/updated) must be already defined.

Query syntax

The query syntax to perform the insert/update operation for a table is as follows.

from <STREAM_NAME> 
select <ATTRIBUTE1_NAME>, <ATTRIBUTE2_NAME>, ...
update or insert into <TABLE_NAME> (for <OUTPUT_EVENT_TYPE>)? 
    set <TABLE_NAME>.<ATTRIBUTE_NAME> = <EXPRESSION>, <TABLE_NAME>.<ATTRIBUTE_NAME> = <EXPRESSION>, ...
    on <CONDITION>

Example

This query matches events from the FooStream stream with the events stored in the StockTable table. When an event in the table has the same value for the symbol attribute as the matching new event from the event stream, it is updated based on the new event. If a new event from the event stream does not have a matching event in the table (i.e., an event with the same value for the symbol attribute), that event is inserted as a new event.

from FooStream
select *
update or insert into StockTable
on StockTable.symbol == symbol