Question

我需要知道如何将2个表连接在一起。我不知道如何加入表格，因为我是新手。

我创建了AnniversaryDBAdapter.class，我在一个数据库中创建了5个表。我只需要加入两个表，如join buddiesList表和喜欢表。

以下是AnniversaryDBAdapter.class的代码

public class AnniversaryDBAdapter
{

    private static final String DATABASE_NAME = "AllTables";
    private static final int DATABASE_VERSION = 2;

    private static final String CREATE_TABLE_BUDDIESLIST = " create table buddiesList(name_id integer primary key autoincrement, name text not null);";
    private static final String CREATE_TABLE_LIKES = " create table likes(name_id integer primary key autoincrement,likes text not null);";
    private static final String CREATE_TABLE_DISLIKES = " create table dislikes(name_id integer primary key autoincrement, dislikes text not null);";
    private static final String CREATE_TABLE_EVENTS = "create table events(date_id integer primary key autoincrement, name_id text not null, date text not null, title_id text not null, starttime text not null, endtime text not null);";
    private static final String CREATE_TABLE_TITLE = "create table titles(title_id integer primary key autoincrement, name text not null, image text not null);";

    private final Context context;
    private static final String TAG = "DBAdapter";

    private DatabaseHelper DBHelper;
    private SQLiteDatabase db;

    public AnniversaryDBAdapter(Context ctx)
    {
        this.context = ctx;
        DBHelper = new DatabaseHelper(context);
    }




private static class DatabaseHelper extends SQLiteOpenHelper
{

    DatabaseHelper(Context context)
    {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(CREATE_TABLE_BUDDIESLIST);
        db.execSQL(CREATE_TABLE_LIKES);
        db.execSQL(CREATE_TABLE_EVENTS);
        db.execSQL(CREATE_TABLE_TITLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {
        Log.w(TAG, "Upgrading database from version "+oldVersion+" to "+newVersion+", which will destroy all old data");

        onCreate(db);

    }

}


public AnniversaryDBAdapter open() throws SQLException
{
    this.db = this.DBHelper.getWritableDatabase();
    return this;
}

public void close()
{
    this.DBHelper.close();
}

}

Answer 1

假设我们将您的表格布局更正为：

CREATE TABLE buddiesList(
    _id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    name TEXT NOT NULL
);

CREATE TABLE likes (
    _id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
    buddy_id INTEGER REFERENCES buddiesList(_id) ON DELETE CASCADE NOT NULL,
    likes TEXT NOT NULL
);

现在，在您的设置中，您可以在VIEW和JOIN之间创建buddiesList likes，在选择时它将像普通表一样 - 您可以不要更新/删除或插入（当然不要乱用TRIGGER）。

CREATE VIEW buddyLikes AS 
    SELECT buddiesList.*, likes._id AS likes_id, likes.likes as likes 
    FROM buddiesList LEFT JOIN likes ON buddiesList._id=likes.buddy_id;

使用View创建execSQL - 就像表格或触发器一样。

通过视图，您可以选择好友和喜欢之间的联接，返回所有好友及其所有喜欢，如下所示：

SELECT * from buddyLikes;

会返回这样的内容：

_id  name   likes_id  likes
1   |Ted   |5        |Facebook
1   |Ted   |4        |Murder
2   |Ed    |1        |Beer
2   |Ed    |2        |Cats 
2   |Ed    |3        |Stock-car racing
3   |Red   |6        |Bananarama

BTW：如果您想在数据库中使用外键支持，则需要致电execSQL 用：

PRAGMA foreign_keys = ON

在SQLiteOpenHelper#onOpen(SQLiteDatabase db)中。

Answer 2

编写查询并使用SQLiteDatabase.rawQuery（sql，params）运行。

如何在SQLiteDatabase中连接两个表？

2 个答案: