Android 如何在SQLiteDatabase中连接两个表?
我需要知道如何将两个表连接在一起。我不知道如何连接表,因为我是新手 我创建了AnniversaryDBAdapter.class,在其中我在一个数据库中创建了5个表。我只需要连接两个表,如join buddiesList表和likes表 下面是AnniversaryDBAdapter.class的代码Android 如何在SQLiteDatabase中连接两个表?,android,database,sqlite,join,Android,Database,Sqlite,Join,我需要知道如何将两个表连接在一起。我不知道如何连接表,因为我是新手 我创建了AnniversaryDBAdapter.class,在其中我在一个数据库中创建了5个表。我只需要连接两个表,如join buddiesList表和likes表 下面是AnniversaryDBAdapter.class的代码 public class AnniversaryDBAdapter { private static final String DATABASE_NAME = "AllTables";
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();
}
}
假设我们将您的表布局更正为以下内容:
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
);
_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
现在,在您的设置中,您可以创建buddiesList和likes之间连接的视图,当选择时,它将像一个普通的表一样-当然,您不能在不使用触发器的情况下从中更新/删除或插入
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;
视图是使用execSQL创建的,就像表或触发器一样
通过视图,您可以从好友和喜欢的人之间的连接中进行选择,返回所有好友及其喜欢的人,如下所示:
SELECT * from buddyLikes;
这将返回如下内容:
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
);
_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
顺便说一句:如果你想在你的数据库中支持外键,你需要调用execSQL
与:
在SQLiteOpenHelperOpenSQLiteDatabase数据库中 编写一个查询并使用SQLiteDatabase.rawQuerysql,params运行。您的buddiesList和likes表实际上没有任何适合加入的内容-如果您打算将name_id作为likes中的外键,则它不应该是自动递增的主键。Ohhh ok。如何通过编码为外键设置name_id。喜欢例如,我在buddiesList中为整型主键自动递增设置了name_id,为text not null设置了name。您通常不会通过编码来实现这一点-最佳做法是使用SQL将其定义为外键-并在buddiesList中的行被删除时,使用诸如级联之类的内置功能来清理likes表。您是说我需要在SQL软件中定义为外键?我使用的是SQLiteDatabase Browser v2.0,但它是用3.6.18版构建的。您所说的像级联这样的内置功能是什么意思?我使用的是EclipseIDEVersion3.7Indigothat工具使用的是一个非常旧的SQLite版本,而外键的语法出现在3.6.18中,直到3.6.19才添加支持。你可能应该考虑自己设计表格——对于像你例子中的小表格来说,这可能更好。你的目标是什么版本的Android?