Java 怎么能ı；从sqlite和外键检索数据

我一直被外键问题困扰，因为通常我可以检索数据，但我不能用外键检索数据

DB.Helper

 public static final String TBL_NAME="users";
    public static final String COL_ID="id";
    public static final String COL_NAME="name";
    public static final String COL_PASS="password";
    public static final String COL_EMAIL="email";
    public static final String COL_PIC="picture";


 public static final String TABLE_NAME = "tasks";
    public static final String C_ID = "_id";
    public static final String TITLE = "title";
    public static final String TYPE = "type";
    public static final String DETAIL = "description";
    public static final String TIME = "time";
    public static final String DATE = "date";
    public static final String KEY_TODO_USER_ID_FK = "userId";



    public static final
    String TBL_QUERY="create table "+TBL_NAME+"("+COL_ID+" INTEGER PRIMARY KEY AUTOINCREMENT,"+COL_NAME+" text,"+COL_PASS+" text,"+COL_EMAIL+" text,"+COL_PIC+" blob)";



    public static final String Task_Query = "create table if not exists " + TABLE_NAME + " ( "
            + C_ID + " integer primary key autoincrement, "
            + TITLE + " text, "
            + DETAIL + " text, "
            + TYPE + " text, "
            + TIME + " text, "
            +  KEY_TODO_USER_ID_FK + " INTEGER REFERENCES " + TBL_NAME + ","
            + DATE + " text)";

查看活动

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + Constants.C_ID + "=" + id, null);
TextView title = (TextView) findViewById(R.id.title);
TextView detail = (TextView) findViewById(R.id.detail);
TextView notetype = (TextView) findViewById(R.id.note_type_ans);
TextView time = (TextView) findViewById(R.id.alertvalue);
TextView date = (TextView) findViewById(R.id.datevalue);
if (cursor != null) {
    if (cursor.moveToFirst()) {
        title.setText(cursor.getString(cursor.getColumnIndex(Constants.TITLE)));
        detail.setText(cursor.getString(cursor.getColumnIndex(Constants.DETAIL)));
        notetype.setText(cursor.getString(cursor.getColumnIndex(Constants.TYPE)));
        time.setText(cursor.getString(cursor.getColumnIndex(Constants.TIME)));
        date.setText(cursor.getString(cursor.getColumnIndex(Constants.DATE)));

    }
    cursor.close();
}

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因此，请帮助我如何仅查看用户任务而不是所有用户任务。

好吧，要仅检索特定用户的数据，您需要在查询中包含该数据。那么这个,

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + Constants.C_ID + "=" + id, null);

应该是这样的：

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + Constants.C_ID + "=" + id + " and " + Constants.KEY_TODO_USER_ID_FK + "=" + userid, null);

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + KEY_TODO_USER_ID_FK  + "=" + userId, null);

---

但是我不知道从哪里得到“userid”变量的值。

列

常量。C\u ID

是

\u ID

是表

常量的自动递增整数主键。表\u NAME

（

任务

）。
您的查询使用它返回一行，该行对应于您在此处用作参数的

id

：

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + Constants.C_ID + "=" + id, null);

如果要使用用户id返回用户的任务，则应如下操作：

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + Constants.C_ID + "=" + id + " and " + Constants.KEY_TODO_USER_ID_FK + "=" + userid, null);

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + KEY_TODO_USER_ID_FK  + "=" + userId, null);

或者更好：

Cursor cursor = sb.rawQuery("select * from " + Constants.TABLE_NAME + " where " + KEY_TODO_USER_ID_FK  + "= ?", new String[] {String.valueOf(userId)});

其中，

userId

是希望获得结果的用户的id。

---

此查询将为该

用户标识返回1行或多行

，但ı不知道如何使put-extra-userId变量