<properties>  
           <property name="hibernate.show_sql" value="true" />         
           <property name="hibernate.hbm2ddl.auto" value="create-drop" />  
</properties>

In fact, the role of this parameter is mainly used: automatically create | update | verify the database table structure. If it is not recommended in this regard the demand for set value = "none".

Several other parameters mean, I explain:

validate load hibernate, the authentication to create a database table structure
create each load hibernate, re-create the database table structure, which is leading to database table data loss reasons.
create-drop to load hibernate create, delete table structure are quit
update loaded hibernate automatically update the database structure



Summary:

1. Please carefully use this parameter, no need not to casually use.

2. If it is found that the database table is missing, please check the configuration of hibernate.hbm2ddl.auto can be set <property name="hibernate.hbm2ddl.auto" value="none" />

3. This setting is suitable ejb configuration file modification