android studio数据库内容增删改查的代码

以下是使用 Android Studio 操作 SQLite 数据库进行增删改查的示例代码：

1. 创建数据库帮助类

public class DatabaseHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "mydatabase.db";
    private static final int DATABASE_VERSION = 1;

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

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_TABLE = "CREATE TABLE mytable ("
                + "id INTEGER PRIMARY KEY AUTOINCREMENT,"
                + "name TEXT,"
                + "age INTEGER)";
        db.execSQL(CREATE_TABLE);
    }

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

2. 插入数据

DatabaseHelper dbHelper = new DatabaseHelper(context);
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", "张三");
values.put("age", 20);
long rowId = db.insert("mytable", null, values);

3. 查询数据

DatabaseHelper dbHelper = new DatabaseHelper(context);
SQLiteDatabase db = dbHelper.getReadableDatabase();
String[] projection = {"id", "name", "age"};
String selection = "age > ?";
String[] selectionArgs = {"18"};
String sortOrder = "age DESC";
Cursor cursor = db.query("mytable", projection, selection, selectionArgs, null, null, sortOrder);
while (cursor.moveToNext()) {
    int id = cursor.getInt(cursor.getColumnIndexOrThrow("id"));
    String name = cursor.getString(cursor.getColumnIndexOrThrow("name"));
    int age = cursor.getInt(cursor.getColumnIndexOrThrow("age"));
    Log.d(TAG, "id: " + id + ", name: " + name + ", age: " + age);
}
cursor.close();

4. 更新数据

DatabaseHelper dbHelper = new DatabaseHelper(context);
SQLiteDatabase db = dbHelper.getWritableDatabase();
ContentValues values = new ContentValues();
values.put("name", "李四");
values.put("age", 21);
String selection = "id = ?";
String[] selectionArgs = {"1"};
int count = db.update("mytable", values, selection, selectionArgs);

5. 删除数据

DatabaseHelper dbHelper = new DatabaseHelper(context);
SQLiteDatabase db = dbHelper.getWritableDatabase();
String selection = "age < ?";
String[] selectionArgs = {"20"};
int count = db.delete("mytable", selection, selectionArgs);