The below table outlines the arithmetic operators available.

The below table outlines the logical and comparison operators available.

The below table outlines the concatenation operators available.

The below table outlines the binary operators available.

The { and } curly braces are array definition operators following the Java array initialization syntax. Arrays can be useful to pass to user-defined functions or to select array data in a select clause.

Array definitions consist of zero or more expressions within curly braces. Any type of expression is allowed within array definitions including constants, arithmetic expressions or event properties. This is the syntax of an array definition:

{ [expression [,expression...]] }

Consider the next statement that returns an event property named actions. The engine populates the actions property as an array of java.lang.String values with a length of 2 elements. The first element of the array contains the observation property value and the second element the command property value of RFIDEvent events.

select {observation, command} as actions from RFIDEvent

The engine determines the array type based on the types returned by the expressions in the array definiton. For example, if all expressions in the array definition return integer values then the type of the array is java.lang.Integer[]. If the types returned by all expressions are compatible number types, such as integer and double values, the engine coerces the array element values and returns a suitable type, java.lang.Double[] in this example. The type of the array returned is Object[] if the types of expressions cannot be coerced or return object values. Null values can also be used in an array definition.

Arrays can come in handy for use as parameters to user-defined functions:

select * from RFIDEvent where Filter.myFilter(zone, {1,2,3})

You can use the dot operator to invoke a method on the result of an expression. The dot operator uses the dot (.) or period character.

The in keyword determines if a given value matches any value in a list. The syntax of the keyword is:

test_expression [not] in (expression [,expression...] )

The test_expression is any valid expression. The keyword is followed by a list of expressions to test for a match. The optional not keyword specifies that the result of the predicate be negated.

The result of an in expression is of type Boolean. If the value of test_expression is equal to any expression from the comma-separated list, the result value is true. Otherwise, the result value is false.

The next example shows how the in keyword can be applied to select certain command types of RFID events:

select * from RFIDEvent where command in ('OBSERVATION', 'SIGNAL')

The statement is equivalent to:

select * from RFIDEvent where command = 'OBSERVATION' or command = 'SIGNAL'

Expression may also return an array, a java.util.Collection or a java.util.Map. Thus event properties that are lists, sets or maps may provide values to compare against test_expression.

All expressions must be of the same type or a compatible type to test_expression. The in keyword may coerce number values to compatible types. If expression returns an array, then the component type of the array must be compatible, unless the component type of the array is Object.

If expression returns an array of component type Object, the operation compares each element of the array, applying equals semantics.

If expression returns a Collection, the operation determines if the collection contains the value returned by test_expression, applying contains semantics.

If expression returns a Map, the operation determines if the map contains the key value returned by test_expression, applying containsKey semantics.

Constants, arrays, Collection and Map expressions or event properties can be used combined.

For example, and assuming a property named 'mySpecialCmdList' exists that contains a list of command strings:

select * from RFIDEvent where command in ( 'OBSERVATION', 'SIGNAL', mySpecialCmdList)

When using prepared statements and substitution parameters with the in keyword, make sure to retain the parenthesis. Substitution values may also be arrays, Collection and Map values:

test_expression [not] in (? [,?...] )

Note that if there are no successes and at least one right-hand row yields null for the operator's result, the result of the any construct will be null, not false. This is in accordance with SQL's normal rules for Boolean combinations of null values.

The between keyword specifies a range to test. The syntax of the keyword is:

test_expression [not] between begin_expression and end_expression

The test_expression is any valid expression and is the expression to test for in the range defined by begin_expression and end_expression. The not keyword specifies that the result of the predicate be negated.

The result of a between expression is of type Boolean. If the value of test_expression is greater then or equal to the value of begin_expression and less than or equal to the value of end_expression, the result is true.

The next example shows how the between keyword can be used to select events with a price between 55 and 60 (endpoints inclusive).

select * from StockTickEvent where price between 55 and 60

The equivalent expression without between is:

select * from StockTickEvent where price >= 55 and price <= 60

And also equivalent to:

select * from StockTickEvent where price between 60 and 55

While the between keyword always includes the endpoints of the range, the in operator allows finer control of endpoint inclusion.

In case the value of begin_expression is less then the value of end_expression the between operator reverses the range.

The following two statements are also equivalent:

select * from StockTickEvent where price between 60 and 55

select * from StockTickEvent where price >= 55 and price <= 60

The like keyword provides standard SQL pattern matching. SQL pattern matching allows you to use '_' to match any single character and '%' to match an arbitrary number of characters (including zero characters). In Esper, SQL patterns are case-sensitive by default. The syntax of like is:

test_expression [not] like pattern_expression [escape string_literal]

The test_expression is any valid expression yielding a String-type or a numeric result. The optional not keyword specifies that the result of the predicate be negated. The like keyword is followed by any valid standard SQL pattern_expression yielding a String-typed result. The optional escape keyword signals the escape character to escape '_' and '%' values in the pattern.

The result of a like expression is of type Boolean. If the value of test_expression matches the pattern_expression, the result value is true. Otherwise, the result value is false.

An example for the like keyword is below.

select * from PersonLocationEvent where name like '%Jack%'

The escape character can be defined as follows. In this example the where-clause matches events where the suffix property is a single '_' character.

select * from PersonLocationEvent where suffix like '!_' escape '!'

The regexp keyword is a form of pattern matching based on regular expressions implemented through the Java java.util.regex package. The syntax of regexp is:

test_expression [not] regexp pattern_expression

The test_expression is any valid expression yielding a String-type or a numeric result. The optional not keyword specifies that the result of the predicate be negated. The regexp keyword is followed by any valid regular expression pattern_expression yielding a String-typed result.

The result of a regexp expression is of type Boolean. If the value of test_expression matches the regular expression pattern_expression, the result value is true. Otherwise, the result value is false.

An example for the regexp keyword is below.

select * from PersonLocationEvent where name regexp '.*Jack.*'

The new operator populates a new data structure by evaluating column names and assignment expressions. This is useful when an expression should return multiple results, for performing a transformation or inside enumeration method lambda expressions.

The synopsis for the new keyword is as follows:

new { column_name = [assignment_expression] [,column_name...] }

The result of the new-operator is a map data structure that contains column_name keys and values. If an assignment expression is provided for a column, the operator evaluates the expression and assigns the result to the column name. If no assignment expression is provided, the column name is assumed to be an event property name and the value is the event property value.

The next statement demonstrates the use of the new operator:

select new {category, price = 2*price} as priceInfo from ProductOrder

The above query returns a single property priceInfo for each arriving ProductOrder event. The property value is itself a map that contains two entries: For the key name category the value of the category property and for the key name price the value of the price property multiplied by two.

The next EPL is an example of the new operator within an expression definition and a case-statement (one EPL statement not multiple):

expression calcPrice {
  productOrder => case
    when category = 'fish' then new { sterialize = 'XRAY', priceFactor = 1.01 }
    when category = 'meat' then new { sterialize = 'UVL', priceFactor = 1 }
  end
}  

select calcPrice(po) as priceDetail from ProductOrder po

In above example the expression calcPrice returns both a sterialize string value and a priceFactor double value. The expression is evaluated as part of the select-clause and the map-type result placed in the priceDetail property pf output events.

When used within the case operator, the operator validates that the data structure is compatible between each case-when result in terms of column names and types. The default value for else in case is null.