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group by clause query

 
Sudarshan Sreenivasan
Ranch Hand
Posts: 188
IntelliJ IDE Java MySQL Database
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The page 216 of Apress - Pro EJB 3 - Java Persistence API
states
The GROUP BY clause defines the grouping expressions over which the results will be aggregated.
A grouping expression must either be a single-valued path expression (state field or
single-valued association field) or an identification variable. If an identification variable is
used, the entity must not have any serialized state or large object fields.



I do not quite get what "serialized state" implies in this context ??

Does it mean that an entity cannot contain properties that implement the Serializable interface ??

Thanks
Sudarshan.
 
It is sorta covered in the JavaRanch Style Guide.
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