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The following functions shipped with Siddhi, consume zero, one or more parameters from streaming events and produce a desired value as output. These functions are executed per event. For more information on Siddhi functions, please refer to Siddhi Query Guide - Functions. More functions are made available as Siddhi Extensions.
eventTimestamp - Returns the timestamp of the processed event
Code Block language sql title eventTimeStamp example from fooStream select symbol as name, eventTimestamp() as eventTimestamp insert into barStream
UUID - Generates a UUID (Universally Unique Identifier)
Code Block language sql title UUID example from fooStream select UUID() as messageID, messageDetails insert into barStream;
default - Checks if the 'attribute' parameter is null and if so returns the value of the 'default' parameter. The function is given as default(<attribute>, <default value>)
Code Block language sql title default example from fooStream select default(temp, 0.0) as temp, roomNum insert into barStream;
cast - Converts the first parameter according to the cast-to parameter. Incompatible arguments cause Class Cast exceptions if further processed.
Code Block language sql title cast example from fooStream select symbol as name, cast(temp, 'double') as temp insert into barStream;
convert - Converts the first input parameter according to the convert-to parameter
Code Block language sql title convert example from fooStream select convert(temp, 'double') as temp insert into barStream;
ifThenElse - Evaluates the 'condition' parameter and returns value of the 'if.expression' parameter if the condition is true, or returns value of the 'else.expression' parameter if the condition is false. The function is given as ifThenElse(<condition>, <if.expression>, <else.expression>)
Code Block language sql title ifThenElse example from fooStream ifThenElse(sensorValue>35,'High','Low') insert into barStream;
minimum - Returns the minimum value of the input parameters
Code Block language sql title minimum example from fooStream select minimum(price1, price2, price3) as minPrice insert into barStream;
- maximum - Returns the maximum value of the input parameters. This function could be used similar to how 'minimum' function is used in a query.
coalesce - Returns the value of the first input parameter that is not null. All input parameters have to be of the same type.
Code Block language sql title coalesce example from fooStream select coalesce('123', null, '789') as value insert into barStream;instanceOfBoolean - Returns 'true' if the input is a instance of Boolean. Otherwise returns 'false'.
Code Block language sql title instanceOfBoolean example from fooStream select instanceOfBoolean(switchState) as state insert into barStream;
- instanceOfDouble - Returns 'true' if the input is a instance of Double. Otherwise returns 'false'. This function could be used similar to how 'instanceOfBoolean' function is used in a query.
- instanceOfFloat - Returns 'true' if the input is a instance of Float. Otherwise returns 'false'. This function could be used similar to how 'instanceOfBoolean' function is used in a query.
- instanceOfInteger - Returns 'true' if the input is a instance of Integer. Otherwise returns 'false'. This function could be used similar to how 'instanceOfBoolean' function is used in a query.
- instanceOfLong - Returns 'true' if the input is a instance of Long. Otherwise returns 'false'. This function could be used similar to how 'instanceOfBoolean' function is used in a query.
- instanceOfString - Returns 'true' if the input is a instance of String. Otherwise returns 'false'. This function could be used similar to how 'instanceOfBoolean' function is used in a query.
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Filters are applied to input data received in streams to filter information based on given conditions. For more information, see Siddhi Query Guide - Filters.
e.g., Filtering cash withdrawals from an ATM machine where the withdrawal amount is greater tha $100, and the withdrawal data is between 01/12/2017-15/12/2017.
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- Events 1-5
- Events 2-6
- Events 3-7
- Events 4-8
- Events 5-9
- Events 6-10
When a batch window is included in a Siddhi query, the folowing event groups are identified:
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This window feature differs from the Defined Window concept elaborated here due to this being specific to a single query only. If a window is to be shared among queries, the Defined Window must be used
For more information about windows, see Siddhi Query Guide - Window.
Aggregate Functions
Aggregation functions allow executing aggregations such as sum, avg, min, etc. on a set of events grouped by a window. If a window is not defined, the aggregation(s) would be calculated by considering all the events arriving at a stream.
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For more information on aggregate function, please refer to Siddhi Query Guide - Aggregate Functions.
Group By
With the group by functionality, events could be grouped based on a certain attribute, when performing aggregations.
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For more information on group by, please refer to Siddhi Query Guide - Group By.
Having
Having allows to filter events after processing the select statement.
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For more information on having clause, please refer to Siddhi Query Guide - Having.
Join
Join is an important feature of Siddhi, which allows combining pair of streams, pair of windows, stream with window, stream/ window with a table and stream/window with an aggregation
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For more information on join queries, please refer to Siddhi Query Guide - Join.
Output Rate Limiting
Output rate limiting allows queries to output events periodically based on a specified condition. This helps to limit continuously sending events as output.
For more information on output rate limiting, please refer to Siddhi Query Guide - Output Rate Limiting
Partitioning
Partitioning in Siddhi allows to logically seperate events arriving at a stream, and to process them separately, in parallel.
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Partitioning can be done based on an attribute value as above, or based on a condition. For more information on partitioning, please refer to Siddhi Query Guide - Partitioning
Trigger
Triggers could be used to get events generated by the system itself, based on some time duration.
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Trigger could be defined as a time interval, a cron job or to generate an event when Siddhi is started. For more information on triggers, please refer to Siddhi Query Guide - Trigger
Script
Scripts allow to define function operations in a different programming language. An example is as follows.
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For more information on scripts, please refer to Siddhi Query Guide - Script