简单查询（推荐）

LambdaQueryWrapper<UserEntitry> lambdaQueryWrapper = new LambdaQueryWrapper();
lambdaQueryWrapper.eq(user.getId() != null, UserEntitry::getId, user.getId());
lambdaQueryWrapper.apply(user.getBeginTime() != null, "UNIX_TIMESTAMP(create_time) >= UNIX_TIMESTAMP('" + user.getBeginTime() + "')");
lambdaQueryWrapper.apply(user.getEndTime() != null, "UNIX_TIMESTAMP(create_time) < UNIX_TIMESTAMP('" + user.getEndTime() + "')");
lambdaQueryWrapper.orderByAsc(UserEntitry::getId);
lambdaQueryWrapper.orderByAsc(UserEntitry::getCreateTime);
PageHelper.startPage(user.getCurrentPage(), user.getPageSize());
List<UserEntitry> list = userEntitryMapper.selectList(lambdaQueryWrapper);

链式查询（不推荐）

List<User> users= new LambdaQueryChainWrapper<>(userService)
                        .eq(User::getUserId, id)
                        .list();

BannerItem bannerItem = new LambdaQueryChainWrapper<>(userService)
                        .eq(User::getUserId, id)
                        .one();

判断条件参考