@Query("SELECT new com.api.projection.GarageVehicleRequestLookupProjection" +
        "(vr.id, vr.appUser.fullName, vr.appUser.unit.id, vr.appUser.unit.name, vr.createdAt, " +
        "vr.startAt, vr.endAt, vr.destination,vr.reason, vr.assignedVehicle.id, " +
        "vr.assignedVehicle.plate, vr.latestAction.vehicleRequestStatus,vr.appUser.unit.director.id, vr.appUser.unit.director.fullName,vr.driverRequested," +
        "vr.garage.name, vr.vehicleTypeRequested, vr.requestType, vr.description, vr.assignedVehicleDriver.id, vr.assignedVehicleDriver.fullName)" +
        " FROM VehicleRequest AS vr " +
        "WHERE " +
        "vr.appUser.fullName like %:fullName% " +
        "AND (coalesce(:unitIds, null) is null or vr.appUser.unit.id in :unitIds) " +
        "AND (coalesce(:garageIds, null) is null or vr.garage.id in :garageIds) " +
        "AND (coalesce(:vehicleIds, null) is null or vr.assignedVehicle.id in :vehicleIds) " +
        "AND (coalesce(:statuses, null) is null or vr.latestAction.vehicleRequestStatus in :statuses) " +
        "AND (coalesce(:createdAt, null) is null or cast(:createdAt as date) = cast(vr.createdAt as date)) " +
        "AND vr.startAt >= :startAt and vr.startAt <= :startAtEnd ")
Page<GarageVehicleRequestLookupProjection> getGarageVehicleRequestsWithFilter(
        @Param("fullName") String fullName,
        @Param("unitIds") List<Long> unitIds,
        @Param("garageIds") List<Long> garageIds,
        @Param("vehicleIds") List<Long> vehicleIds,
        @Param("statuses") List<VehicleRequestStatus> status,
        @Param("createdAt") Date createdAt,
        @Param("startAt") Date startAt, @Param("startAtEnd") Date startAtEnd,
        Pageable pageable);

VehicleRequest表中有146条记录。当我运行上面的hql语句时，如果vr.assignedVehicle为空，则不会返回记录，因此我得到36条记录，因为只有这些记录具有assignedVehicle（assignedVehicleId）。
当我不像这样做投影的时候，

SELECT vr FROM VehicleRequest AS vr ...

所有的记录都将被返回。上述方法的问题是有太多的连接，因此JPA对数据库发出太多的请求。
这是在删除了一些不必要的条件后生成的语句，

select vehiclereq0_.id                         as col_0_0_,
       appuser1_.full_name                     as col_1_0_,
       appuser1_.unit_id                       as col_2_0_,
       unit4_.name                             as col_3_0_,
       vehiclereq0_.created_at                 as col_4_0_,
       vehiclereq0_.start_at                   as col_5_0_,
       vehiclereq0_.end_at                     as col_6_0_,
       vehiclereq0_.destination                as col_7_0_,
       vehiclereq0_.reason                     as col_8_0_,
       vehiclereq0_.assigned_vehicle_id        as col_9_0_,
       vehicle5_.plate                         as col_10_0_,
       vehiclereq6_.vehicle_request_status     as col_11_0_,
       unit4_.director_id                      as col_12_0_,
       appuser11_.full_name                    as col_13_0_,
       vehiclereq0_.driver_requested           as col_14_0_,
       garage12_.name                          as col_15_0_,
       vehiclereq0_.vehicle_type_requested     as col_16_0_,
       vehiclereq0_.request_type               as col_17_0_,
       vehiclereq0_.description                as col_18_0_,
       vehiclereq0_.assigned_vehicle_driver_id as col_19_0_,
       appuser13_.full_name                    as col_20_0_
from vehicle_request vehiclereq0_
         cross join app_user appuser1_
         cross join unit unit4_
         cross join app_user appuser11_
         cross join vehicle vehicle5_
         cross join vehicle_request_action vehiclereq6_
         cross join garage garage12_
         cross join app_user appuser13_
where vehiclereq0_.app_user_id = appuser1_.id
  and appuser1_.unit_id = unit4_.id
  and unit4_.director_id = appuser11_.id
  and vehiclereq0_.latest_action_id = vehiclereq6_.id
  and vehiclereq0_.garage = garage12_.id
  and vehiclereq0_.assigned_vehicle_driver_id = appuser13_.id
  and vehiclereq0_.assigned_vehicle_id = vehicle5_.id
  and (coalesce(null, null) is null or appuser1_.unit_id in (null))
  and (coalesce(null, null) is null or vehiclereq0_.garage in (null))
  and (coalesce(null, null) is null or vehiclereq0_.assigned_vehicle_id in (null))
  and (coalesce(null, null) is null or vehiclereq6_.vehicle_request_status in (null))
order by vehiclereq0_.created_at desc

这些语句可以为空，

and vehiclereq0_.assigned_vehicle_driver_id = appuser13_.id
and vehiclereq0_.assigned_vehicle_id = vehicle5_.id