@Table is set at the class level; it allows you to define the table, catalog, and schema names for your entity bean mapping. If no @Table is defined the default values are used: the unqualified class name of the entity.

@Entity
@Table(name="tbl_sky")
public class Sky implements Serializable {
...
            

The @Table element also contains a schema and a catalog attributes, if they need to be defined. You can also define unique constraints to the table using the @UniqueConstraint annotation in conjunction with @Table (for a unique constraint bound to a single column, refer to @Column).

@Table(name="tbl_sky",
    uniqueConstraints = {@UniqueConstraint(columnNames={"month", "day"})}
)

A unique constraint is applied to the tuple month, day. Note that the columnNames array refers to the logical column names.

The logical column name is defined by the Hibernate NamingStrategy implementation. The default EJB3 naming strategy use the physical column name as the logical column name. Note that this may be different than the property name (if the column name is explicit). Unless you override the NamingStrategy, you shouldn't worry about that.