Android studio中的SQL数据库的增删查改

在 Android Studio 中，可以使用 SQLite 数据库进行数据存储和管理。下面是使用 SQL 数据库进行增删查改的示例代码：

## 建表

public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "my_database";
    private static final int DB_VERSION = 1;
    private static final String TABLE_NAME = "my_table";
    private static final String COLUMN_ID = "_id";
    private static final String COLUMN_NAME = "name";
    private static final String COLUMN_AGE = "age";

    public MyDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String createTableSql = "CREATE TABLE " + TABLE_NAME + " ("
                + COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
                + COLUMN_NAME + " TEXT,"
                + COLUMN_AGE + " INTEGER)";
        db.execSQL(createTableSql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String dropTableSql = "DROP TABLE IF EXISTS " + TABLE_NAME;
        db.execSQL(dropTableSql);
        onCreate(db);
    }
}

## 插入数据

public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new MyDatabaseHelper(this);
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(MyDatabaseHelper.COLUMN_NAME, "张三");
        values.put(MyDatabaseHelper.COLUMN_AGE, 18);
        db.insert(MyDatabaseHelper.TABLE_NAME, null, values);

        db.close();
    }
}

## 查询数据

public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new MyDatabaseHelper(this);
        SQLiteDatabase db = dbHelper.getReadableDatabase();

        Cursor cursor = db.query(MyDatabaseHelper.TABLE_NAME, null, null, null, null, null, null);
        while (cursor.moveToNext()) {
            int id = cursor.getInt(cursor.getColumnIndex(MyDatabaseHelper.COLUMN_ID));
            String name = cursor.getString(cursor.getColumnIndex(MyDatabaseHelper.COLUMN_NAME));
            int age = cursor.getInt(cursor.getColumnIndex(MyDatabaseHelper.COLUMN_AGE));
            Log.d("MainActivity", "id=" + id + ", name=" + name + ", age=" + age);
        }
        cursor.close();

        db.close();
    }
}

## 更新数据

public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new MyDatabaseHelper(this);
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(MyDatabaseHelper.COLUMN_AGE, 20);
        db.update(MyDatabaseHelper.TABLE_NAME, values, MyDatabaseHelper.COLUMN_NAME + "=?", new String[]{"张三"});

        db.close();
    }
}

## 删除数据

public class MainActivity extends AppCompatActivity {
    private MyDatabaseHelper dbHelper;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        dbHelper = new MyDatabaseHelper(this);
        SQLiteDatabase db = dbHelper.getWritableDatabase();

        db.delete(MyDatabaseHelper.TABLE_NAME, MyDatabaseHelper.COLUMN_NAME + "=?", new String[]{"张三"});

        db.close();
    }
}