@DiscriminatorColumn(name = "discrim", discriminatorType = DiscriminatorType.INTEGER)
@Entity
@Inheritance(strategy = SINGLE_TABLE)
@Table(name = "BASE_TABLE")
public abstract class BaseTable {
}

@DiscriminatorValue("1")
@Entity
@SecondaryTables({
  @SecondaryTable(name = "MANDATORY_TABLE"),
  @SecondaryTable(name = "OPTIONAL_TABLE_1", pkJoinColumns = @PrimaryKeyJoinColumn(name = "PK1")),
  @SecondaryTable(name = "OPTIONAL_TABLE_2", pkJoinColumns = @PrimaryKeyJoinColumn(name = "PK2"))
})
@Tables({
  @Table(appliesTo = "mandatory_table", fetch = FetchMode.SUBSELECT, optional = false),
  @Table(appliesTo = "optional_table_1", fetch = FetchMode.SUBSELECT, optional = true),
  @Table(appliesTo = "optional_table_2", fetch = FetchMode.SUBSELECT, optional = true)
})
public abstract class Inherited extends BaseTable {
}

select
  ...
from
  mandatory_table mandatory_table_17_
  left outer join optional_table_2 optional_table_2_16_ on optional_table_2_16_.PK2=mandatory_table_17_.PK
  left outer join optional_table_1 optional_table_1_18_ on optional_table_2_16_.PK2=optional_table_1_18_.PK1
where
  mandatory_table_17_.PK2=?

select
...
from
  optional_table_2 optional_table_2_16_
  inner join mandatory_table mandatory_table_17_ on optional_table_2_16_.PK2=mandatory_table_17_.PK
  left outer join optional_table_1 optional_table_1_18_ on optional_table_2_16_.PK2=optional_table_1_18_.PK1
where 
  optional_table_2_16_.PK2=?