This chapter provides a reference to functions in Event Processing Language (EPL). Note that EPL is deprecated; new development should use Oracle Continuous Query Language (Oracle CQL).
This chapter includes the following sections:
Singlerow functions return a single value for every single result row generated by your statement. These functions can appear anywhere where expressions are allowed.
EPL allows static Java library methods as singlerow functions, and also features builtin singlerow functions.
EPL autoimports the following Java library packages:
java.lang.*
java.math.*
java.text.*
java.util.*
Thus Java static library methods can be used in all expressions as shown in below example:
SELECT symbol, Math.round(volume/1000) FROM StockTickEvent RETAIN 30 SECONDS
Other arbitrary Java classes may also be used, however their names must be fully qualified or configured to be imported. For more information, see Section 4.3, "UserDefined functions."
The table below outlines the builtin singlerow functions available.
Table 41 BuiltIn SingleRow Functions
Singlerow Function  Result  See 

MAX(expression, expression [, expression [,…])

Returns the highest numeric value among the two or more commaseparated expressions. 

MIN(expression, expression [, expression [,…])

Returns the lowest numeric value among the two or more commaseparated expressions. 

COALESCE(expression, expression [, expression [,…])

Returns the first nonnull value in the list, or null if there are no nonnull values. 

CASE value
WHEN compare_value THEN result
[WHEN compare_value THEN result …]
[ELSE result]
END

Returns result where the first value equals 

CASE value
WHEN condition THEN result
[WHEN condition THEN result …]
[ELSE result]
END

Returns the result for the first condition that is true. 

PREV(expression, event_property)

Returns a property value of a previous event, relative to the event order within a data window. 

PRIOR(integer, event_property)

Returns a property value of a prior event, relative to the natural order of arrival of events 

SELECT
CASE
WHEN INSTANCEOF(item, com.mycompany.Service) THEN serviceName?
WHEN INSTANCEOF(item, com.mycompany.Product) THEN productName?
END
FROM OrderEvent

Returns a 

SELECT CAST(item.price?, double) FROM OrderEvent

Casts the return type of an expression to a designated type. 

SELECT EXISTS(item.serviceName?) FROM OrderEvent

Returns a boolean value indicating whether the dynamic property, provided as a parameter to the function, exists on the event. 
You may also create userdefined singlerow functions. See Section 4.3, "UserDefined functions".
The MIN
and MAX
functions take two or more expression parameters. The MIN
function returns the lowest numeric value among these commaseparated expressions, while the MAX
function returns the highest numeric value. The return type is the compatible aggregated type of all return values.
The next example shows the MAX
function that has a Double
return type and returns the value 1.1
.
SELECT MAX(1, 1.1, 2 * 0.5) FROM ...
The MIN
function returns the lowest value. The statement below uses the function to determine the smaller of two timestamp values.
SELECT symbol, MIN(ticks.timestamp, news.timestamp) AS minT FROM StockTickEvent AS ticks, NewsEvent AS news RETAIN 30 SECONDS WHERE ticks.symbol = news.symbol
The MIN
and MAX
functions are also available as aggregate functions. See Section 4.2, "Aggregate functions" for a description of this usage.
The result of the COALESCE
function is the first expression in a list of expressions that returns a nonnull value. The return type is the compatible aggregated type of all return values.
This example returns a String
type result with a value of foo
.
SELECT COALESCE(NULL, 'foo') FROM …
The CASE
control flow function has two versions. The first version takes a value and a list of compare values to compare against, and returns the result where the first value equals the compare value. The second version takes a list of conditions and returns the result for the first condition that is true.
The return type of a CASE
expression is the compatible aggregated type of all return values.
The example below shows the first version of a CASE
statement. It has a String
return type and returns the value one
.
SELECT CASE 1 WHEN 1 THEN 'one' WHEN 2 THEN 'two' ELSE 'more' END FROM …
The second version of the CASE
function takes a list of conditions. The next example has a Boolean
return type and returns the Boolean
value true
.
SELECT CASE WHEN 1>0 THEN true ELSE false END FROM …
The PREV
function returns the property value of a previous event. The first parameter denotes the i^{th} previous event in the order established by the data window. The second parameter is a property name for which the function returns the value for the previous event.
This example selects the value of the price property of the second previous event from the current Trade
event.
SELECT PREV(2, price) FROM Trade RETAIN 10 EVENTS
Because the PREV
function takes the order established by the data window into account, the function works well with sorted windows. In the following example the statement selects the symbol of the three Trade events that had the largest, secondlargest and thirdlargest volume.
SELECT PREV(0, symbol), PREV(1, symbol), PREV(2, symbol) FROM Trade RETAIN 10 EVENTS WITH LARGEST volume
The i^{th} previous event parameter can also be an expression returning an Integer
type value. The next statement joins the Trade
data window with a RankSelectionEvent
event that provides a rank property used to look up a certain position in the sorted Trade
data window:
SELECT PREV(rank, symbol) FROM Trade, RankSelectionEvent RETAIN 10 EVENTS WITH LARGEST volume
The PREV
function returns a NULL value if the data window does not currently hold the i^{th} previous event. The example below illustrates this using a time batch window. Here the PREV
function returns a null value for any events in which the previous event is not in the same batch of events. The PRIOR
function as discussed below can be used if a null value is not the desired result.
SELECT PREV(1, symbol) FROM Trade RETAIN BATCH OF 1 MINUTE
The combination of the PREV
function and the PARTITION BY
clause returns the property value for a previous event in the given group.
For example, assume we want to obtain the price of the previous event of the same symbol as the current event.
The statement that follows solves this problem. It partitions the window on the symbol property over a time window of one minute. As a result, when the engine encounters a new symbol value that it hasn't seen before, it creates a new window specifically to hold events for that symbol. Consequently, the PREV
function returns the previous event within the respective time window for that event's symbol value.
SELECT PREV(1, price) AS prevPrice FROM Trade RETAIN 1 MIN PARTITION BY symbol
The PRIOR
function returns the property value of a prior event. The first parameter is an integer value that denotes the ith prior event in the natural order of arrival. The second parameter is a property name for which the function returns the value for the prior event.
This example selects the value of the price property of the second prior event to the current Trade
event.
SELECT PRIOR(2, price) FROM Trade RETAIN ALL
The PRIOR
function can be used on any event stream or view and does not require a stream to be constrained by a RETAIN
clause as with the PREV
function. The function operates based on the order of arrival of events in the event stream that provides the events.
The next statement uses a length batch window to compute an average volume for every 3 Trade
events, posting results every 3 events. The SELECT
clause employs the PRIOR
function to select the current average and the average before the current average:
SELECT AVG(volume) AS avgVolume, AVG(PRIOR(3, volume)) FROM Trade RETAIN BATCH OF 3 EVENTS
The PRIOR
function is similar to the PREV
function. The key differences between the two functions are as follows:
The PREV
function returns previous events in the order provided by the window, while the PRIOR
function returns prior events in the order of arrival in the stream.
The PREV
function requires a RETAIN
clause while the PRIOR
function does not.
The PREV
function returns the previous event taking into account any grouping. The PRIOR
function returns prior events regardless of any grouping.
The PREV
function returns a null value for remove stream events, i.e. for events leaving a data window. The PRIOR
function does not have this restriction.
The INSTANCEOF
function returns a boolean value indicating whether the type of value returned by the expression is one of the given types. The first parameter to the INSTANCEOF
function is an expression to evaluate. The second and subsequent parameters are Java type names.
The INSTANCEOF
function determines the return type of the expression at runtime by evaluating the expression, and compares the type of object returned by the expression to the defined types. If the type of object returned by the expression matches any of the given types, the function returns true. If the expression returned null or a type that does not match any of the given types, the function returns false.
The INSTANCEOF
function is often used in conjunction with dynamic (unchecked) properties. Dynamic properties are properties whose type is not known at compile type.
The following example uses the INSTANCEOF
function to select different properties based on the type:
SELECT CASE WHEN INSTANCEOF(item, com.mycompany.Service) THEN serviceName? WHEN INSTANCEOF(item, com.mycompany.Product) THEN productName? END FROM OrderEvent
The INSTANCEOF
function returns false if the expression tested by INSTANCEOF
returned null.
Valid parameters for the type parameter are:
Any of the Java builtin types: int
, long
, byte
, short
, char
, double
, float
, string
, where string
is a short notation for java.lang.String
. The type name is not casesensitive. For example, the following function tests if the dynamic price
property is either of type float
or type double
:
INSTANCEOF(price?, double, float)
The fullyqualified class name of the class to test, for example:
INSTANCEOF(product, org.myproducer.Product)
Valid parameters for the type parameter list are:
The INSTANCEOF
function considers an event class's superclasses as well as all the directly or indirectlyimplemented interfaces by superclasses.
The CAST
function casts the return type of an expression to a designated type. The function accepts two parameters: the first parameter is the property name or expression that returns the value to be casted and the second parameter is the type to cast to.
Valid parameters for the second (type) parameter are:
Any of the Java builtin types: int
, long
, byte
, short
, char
, double
, float
, string
, where string
is a short notation for java.lang.String
. The type name is not casesensitive. For example:
cast(price, double)
The fullyqualified class name of the class to cast to, for example:
cast(product, org.myproducer.Product)
The CAST
function is often used to provide a type for dynamic (unchecked) properties. Dynamic properties are properties whose type is not known at compile type. These properties are always of type java.lang.Object
.
The following example shows how to use the CAST
function to cast the price
dynamic property of an item
in the OrderEvent
to a double
value.
SELECT CAST(item.price?, double) FROM OrderEvent
The CAST
function returns a null value if the expression result cannot be casted to the desired type, or if the expression result itself is null.
The CAST
function adheres to the following type conversion rules:
For all numeric types, the CAST
function utilizes java.lang.Number
to convert numeric types, if required.
For casts to string
or java.lang.String
, the CAST
function calls toString
on the expression result.
For casts to other objects, including application objects, the CAST
function considers a Java class's superclasses as well as all directly or indirectlyimplemented interfaces by superclasses .
The EXISTS
function returns a boolean value indicating whether the dynamic property, provided as a parameter to the function, exists on the event. The EXISTS
function accepts a single dynamic property name as its only parameter.
Use the EXISTS
function with dynamic (unchecked) properties. Dynamic properties are properties whose type is not known at compile type. Dynamic properties return a null value if the dynamic property does not exist on an event, or if the dynamic property exists but the value of the dynamic property is null.
The following example of using the EXISTS
function returns true if the item
property contains an object that has a serviceName
property. It returns false if the item
property is null, or if the item
property does not contain an object that has a property named serviceName
:
SELECT EXISTS(item.serviceName?) FROM OrderEvent
The aggregate functions are SUM
, AVG
, COUNT
, MAX
, MIN
, MEDIAN
, STDDEV
, AVEDEV
. You can use aggregate functions to calculate and summarize data from event properties. For example, to find out the total price for all stock tick events in the last 30 seconds:
SELECT SUM(price) FROM StockTickEvent RETAIN 30 SECONDS
Here is the syntax for aggregate functions:
aggregate_function( [ALL  DISTINCT] expression)
You can apply aggregate functions to all events in an event stream window or other view, or to one or more groups of events. From each set of events to which an aggregate function is applied, EPL generates a single value.
The expression is usually an event property name. However it can also be a constant, function, or any combination of event property names, constants, and functions connected by arithmetic operators.
For example, to find out the average price for all stock tick events in the last 30 seconds if the price was doubled:
SELECT AVG(price * 2) FROM StockTickEvent RETAIN 30 SECONDS
You can use the optional keyword DISTINCT
with all aggregate functions to eliminate duplicate values before the aggregate function is applied. The optional keyword ALL
which performs the operation on all events is the default.
The MIN
and MAX
aggregate functions are also available as single row functions. See Section 4.1.1, "The MIN and MAX Functions" for a description of this usage.
The syntax of the aggregation functions and the results they produce are shown in table below.
Aggregate Function  Result 

SUM([ALLDISTINCT] expression) 
Totals the (distinct) values in the 
AVG([ALLDISTINCT] expression) 
Average of the (distinct) values in the 
COUNT([ALLDISTINCT] expression) 
Number of the (distinct) nonnull values in the 
COUNT(*) 
Number of events, returning a value of 
MAX([ALLDISTINCT] expression) 
Highest (distinct) value in the 
MIN([ALLDISTINCT] expression) 
Lowest (distinct) value in the 
MEDIAN([ALLDISTINCT] expression) 
Median (distinct) value in the 
STDDEV([ALLDISTINCT] expression) 
Standard deviation of the (distinct) values in the Oracle Event Processing uses a common measure called sample standard deviation when internally implementing STDDEV, rather than the precise mathematical definition. The definition used by Oracle Event Processing for STDDEV is as follows: stddev(x) = (1/(N1) * SUM{i=1 ... n}(xi  xavg) ) ^ (1/2) 
AVEDEV([ALLDISTINCT] expression) 
Mean deviation of the (distinct) values in the Oracle Event Processing uses the following definition for AVEDEV: avedev(x) = 1/n * SUM{i=1 . . . n} (x_i ? xavg) 
TREND(expression) 
Number of consecutive up ticks (as positive number), down ticks (as negative number), or no change (as zero) for 
You can use aggregation functions in a SELECT
clause and in a HAVING
clause. You cannot use aggregate functions in a WHERE
clause, but you can use the WHERE
clause to restrict the events to which the aggregate is applied. The next query computes the average and sum of the price of stock tick events for the symbol ACME
only, for the last 10 stock tick events regardless of their symbol.
SELECT 'ACME stats' AS title, AVG(price) AS avgPrice, SUM(price) AS sumPrice FROM StockTickEvent RETAIN 10 EVENTS WHERE symbol='ACME'
In the preceding example the length window of 10 elements is not affected by the WHERE
clause, in other words, all events enter and leave the length window regardless of their symbol. If we only care about the last 10 ACME
events, we need to add a MATCHING
clause as shown below.
SELECT 'ACME stats' AS title, AVG(price) AS avgPrice, SUM(price) AS sumPrice FROM (SELECT * FROM StockTickEvent WHERE symbol='ACME') RETAIN 10 EVENT
You can use aggregate functions with any type of event property or expression, with the following restriction:
You can use SUM
, AVG
, MEDIAN
, STDDEV
, AVEDEV
with numeric event properties only
EPL ignores any null values returned by the event property or expression on which the aggregate function is operating, except for the COUNT(*)
function, which counts null values as well. All aggregate functions return null if the data set contains no events, or if all events in the data set contain only null values for the aggregated expression.
You may also create an aggregate userdefined function. For more information, see Section 4.3, "UserDefined functions".
A userdefined function can be invoked anywhere as an expression itself or within an expression. The function must simply be a public static method that the class loader can resolve at statement creation time. The engine resolves the function reference at statement creation time and verifies parameter types.
Caution:
Only idempotent userdefined functions in EPL queries are allowed. That is, multiple invocations of the userdefined function does not change the result.
The example below assumes a class MyClass
that exposes a public static method myFunction
accepting two parameters, and returning a numeric type such as double
.
SELECT 3 * MyClass.myFunction(price, volume) as myValue FROM StockTick RETAIN 30 SECONDS
Userdefined functions also take array parameters as this example shows. Section 3.6, "Array Definition Operator" outlines in more detail the types of arrays produced.
SELECT * FROM RFIDEvent RETAIN 10 MINUTES WHERE com.mycompany.rfid.MyChecker.isInZone(zone, {10, 20, 30})
Oracle Event Processing supports both singlerow and aggregate userdefined functions.
For more information, see "wlevs:function" in the Oracle Fusion Middleware Developer's Guide for Oracle Event Processing for Eclipse.