If you are using EclipseLink (2.1) you can use the FUNC() function to call any database function that is not defined in the JPA JPQL spec.
i.e.
FUNC('MONTH', c_Date)
In JPA 2.1 (EclipseLink 2.5) the FUNCTION syntax becomes part of the specification (and replaces the EclipseLink-specific FUNC).
If you are using TopLink Essentials, you cannot do this in JPQL, but you can define a TopLink Expression query for it (similar to JPA 2.0 criteria), or use native SQL.
Also if you are using any JPA 2.0 provider and using a Criteria query there is a function() API that can be used to define this.
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