如何删除Android下一版空间数据库中的列？

@Database(entities = {User.class, AdTime.class}, version = 1, exportSchema = false)
  public abstract class AppDataBase extends RoomDatabase {

  private static AppDataBase INSTANCE;

  public abstract UserDao userModel();

  public abstract AdDao adModel();

  public static AppDataBase getInMemoryDatabase(Context context) {

    if (INSTANCE == null) {
        INSTANCE = Room.databaseBuilder(context, AppDataBase.class, "adrider")
                // To simplify the codelab, allow queries on the main thread.
                // Don't do this on a real app! See PersistenceBasicSample for an example.
                .allowMainThreadQueries()
              //  .addMigrations(MIGRATION_1_2)
                //  .fallbackToDestructiveMigration()
                .build();
      }
      return INSTANCE;
    }

  static final Migration MIGRATION_1_2=new Migration(1,2) {
      @Override
      public void migrate(@NonNull SupportSQLiteDatabase database) {
          database.execSQL("ALTER TABLE User "
                + "DROP Download");
      }
  };

}

database.execSQL("CREATE TABLE t1_backup AS SELECT a, b FROM t1");
database.execSQL("DROP TABLE t1");
database.execSQL("ALTER TABLE t1_backup RENAME TO t1");

显然,更改表名称和列名称以适合您的方案.