字段为空时的 Android 房间顺序

Question

我使用 Room Persistence Library 来存储联系信息。 我想根据姓氏和名字检索联系人。

问题是没有姓氏和名字 ( null ) 的联系人被接收到列表的顶部。 如何查询以使它们位于列表底部？

这是我的查询：

select * from CacheContact order by lastName asc,firstName asc LIMIT :count OFFSET :offset

CacheContact 对象：

@Entity
public class CacheContact {

    private String expireDate;

    @PrimaryKey
    private long id;
    private String firstName;
    private long userId;
    private String lastName;
    private Boolean blocked;
    private long creationDate;
    private String profileImage;

    @Embedded
    private LinkedUser linkedUser;
    private String cellphoneNumber;
    private String email;
    private String uniqueId;
    private long notSeenDuration;
    private boolean hasUser;

全道法：

@Query("select * from CacheContact order by lastName asc,firstName asc LIMIT :count OFFSET :offset")
    List<CacheContact> getContacts(Integer count, Long offset);

Answer 1

试试这样：

select * from CacheContact order by lastName is null or lastName='', lastName, firstName is null or firstName='', firstName LIMIT :count OFFSET :offset

上述查询还检查空字符串值。

从SQLite Release 3.30.0 开始，你也可以使用NULLS LAST，所以你可以这样做：

select * from table order by column_name NULLS LAST;

Answer 2

select * from CacheContact 
order by case when lastName is null or firstName is null then 1 else 0 end, 
lastName asc, firstName asc LIMIT :count OFFSET :offset