Apama 10.3 | Apama Documentation | Developing Apama Applications | EPL Reference | Events and Event Listeners | Event templates | By-name qualifiers
By-name qualifiers
A by-name qualifier names an event field whose value is to be matched, instead of matching by position.
The identifier must be the name of one of the event's fields. The field's type must be integer, decimal, float, or string. Each event field is allowed to appear only once on the left side of a by-name qualifier, and the same field is not allowed in both a by-position qualifier and a by-name qualifier in the same event template.
An example of a by-name qualifier list is as follows (see the example in By-position qualifiers for the event fields that are also used for this example):
sample1 (itemName="eggs", price=0.50, quantity=3)
If the qualifier uses = *, then the qualifier matches all possible values of the specified event field.
If the qualifier uses one of the relational operators < (less than), <= (less than or equal to), > (greater than), >= (greater than or equal to), and = (equal to), then the event field value is compared with the event template's value, and a match occurs when the result of the comparison is true.
If the qualifier uses in followed by a range expression, then the field is compared against the boundary values of the range.
The expression or range expression on the right side is not allowed to refer to any of the event's fields.
The expression or range expression is evaluated once, when the on statement containing the template is executed and its event expressions evaluated, not each time an event of the same type is processed by the correlator.

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