SQLite数据库_sqllistopenhelper有几个方法

1.sqlLiteOpenHelper 抽象类 需要创建一个自己的帮助类取继承它
2.sqlLiteOpenHelper 有2个抽象方法，onCreate 和 onUpgrade 分别实现创建和升级 数据库
3.sqlLiteOpenHelper 2个实例方法 ， getReadableDatabase 和getWritableDatabase 创建或者打开一个数据库（数据库存在则打开，不存在则创建）
返回可对数据库进行读写的对象；
4.sqlLiteOPenHelper 中2个构造方法可重写，采用4个参数的
第一个参数：Context
第二：数据库名
第三：查询数据时候返回一个自定义Cursor，一般传null
第四：数据库版本号

onCreate 用于处理一些创建表的 操作

5.创建数据库

创建MyDatabaseHelper 类继承SQLiteOpenHelper 

public class MyDatabaseHelper extends SQLiteOpenHelper
{
    // 建表语句
    public static final String CREATE_BOOK = "create table book ( "
        + "id integer primary key autoincrement, "
        + "author text,"
        + "price real,"
        + "pages integer,"
        + "name text)";
 
    private Context mContext;
 
    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)
    {
        super(context, name, factory, version);
        mContext = context;
    }
 
    @Override
    public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(CREATE_BOOK);
 
    }
 
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {
 
    }
}

public class MainActivity extends AppCompatActivity
{
 
    private MyDatabaseHelper dbHelper;
 
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // 创建数据库
        dbHelper = new MyDatabaseHelper(this,"tableName.db",null,1);
        dbHelper.getWritableDatabase();
    }
}

6.升级数据

public class MyDatabaseHelper extends SQLiteOpenHelper
{
    // 建表语句
    public static final String CREATE_BOOK = "create table book ( "
        + "id integer primary key autoincrement, "
        + "author text,"
        + "price real,"
        + "pages integer,"
        + "name text)";
    // 多加一张表
    public static final String CREATE_PERSON = "create table person( "
        + "id integer primary key autoincrement,"
        + "name text,"
        + "age integer,"
        + "sex text)";
 
    private Context mContext;
 
    public MyDatabaseHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)
    {
        super(context, name, factory, version);
        mContext = context;
    }
 
    @Override
    public void onCreate(SQLiteDatabase db)
    {
        db.execSQL(CREATE_BOOK);
        db.execSQL(CREATE_PERSON);
    }
 
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
    {
       // 先调用 如果发现数据库中存在book 和person表，则先删除2张表后再调用onCreate方法重新创建2表
        db.execSQL("drop table if exists Book");
        db.execSQL("drop table if exists Person");
        onCreate(db);
    }
}

public class MainActivity extends AppCompatActivity
{
 
    private MyDatabaseHelper dbHelper;
 
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        // 升级数据库
        dbHelper = new MyDatabaseHelper(this,"tableName.db",null,2);
        dbHelper.getWritableDatabase();
    }
}

7.insert 数据

先获取SQLiteDataBase对象

再使用ContentValues 对数据进行封装

        // insert数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values =new ContentValues();
        // 添加数据
        values.put("name","haha");
        values.put("age",12);
        db.insert("表名",null,values);

8.update数据

        // update数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        ContentValues values =new ContentValues();
        // 添加数据
        values.put("name","haha");
        db.update("表名",values,"id = ?",new String[]{"1"});

9.delete数据

        // delete数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        // 删除数据
        db.delete("表名","id = ?",new String[] {"1"});

10.select

        // 查询数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        // 表名，指定查询的咧名，where的约束条件，为where站位符提供值，指定group by的咧，对结果进一步约束，指定查询结果的排序
        Cursor cursor = db.query("表名", null, null, null, null, null, null);
        // 便利Cursor 取出数据
        if (cursor.moveToFirst()) {
            do {
                String name = cursor.getString(cursor.getColumnIndex("name"));
            } while (cursor.moveToNext());
        }

11. 使用sql语句操作数据库

        // 查询数据
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        // 使用sql操作数据库
        db.execSQL("sql语句");
        // 只有select的时候使用rawQuery
        db.rawQuery("select * from Book",null);