如何在android上的Query中添加WHERE子句

// 创建一个SQLiteOpenHelper类
public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "mydatabase.db";
    private static final int DATABASE_VERSION = 1;

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建表结构
        String createTableQuery = "CREATE TABLE mytable (id INTEGER PRIMARY KEY, name TEXT)";
        db.execSQL(createTableQuery);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 升级数据库版本时的操作
    }
}

// 在需要执行查询的地方
MyDatabaseHelper dbHelper = new MyDatabaseHelper(context);
SQLiteDatabase db = dbHelper.getReadableDatabase();

// 定义查询的列和表名
String[] projection = {
    "id",
    "name"
};

// 定义WHERE子句
String selection = "name = ?";
String[] selectionArgs = {"John"};

// 执行查询操作
Cursor cursor = db.query(
    "mytable",  // 表名
    projection, // 查询的列
    selection,  // WHERE子句
    selectionArgs,  // WHERE子句的参数
    null,
    null,
    null
);

// 遍历查询结果
while (cursor.moveToNext()) {
    int id = cursor.getInt(cursor.getColumnIndexOrThrow("id"));
    String name = cursor.getString(cursor.getColumnIndexOrThrow("name"));
    // 处理查询结果
}

// 关闭Cursor和数据库连接
cursor.close();
db.close();