字段为空时的 Android 房间顺序

Question

我用 房间持久性库 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 )的联系人在列表顶部收到。
如何查询以使它们位于列表的底部？

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

上面的查询还检查空字符串值。

来自 SQLite Release 3.30.0之后，您也可以使用 NULLS LAST ，因此您可以执行以下操作:

select * from table order by column_name NULLS LAST;