查询表中数据的两种方法（select查）

Posted 2020-09-04 懂你在爱我

1.通过点击按钮来执行查询表中数据。（数据库和表的创建不在详细介绍，请自动阅读数据库和表的创建）

第一种方法：直接使用SQL来操作数据库，调用execSQL(sql)语句

public class MainActivity extends AppCompatActivity {
    private Button mSelectButton;
    private mysqliteHelper mMySqliteHelper;
    private SQLiteDatabase db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mMySqliteHelper = DbManger.getIntance(MainActivity.this);
        mSelectButton = (Button) findViewById(R.id.select_btn);
        //点击按钮查询数据
        mSelectButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                db = mMySqliteHelper.getWritableDatabase();
                String sql = "select * from "+Constant.TABLE_NAME+ " where "+Constant.ID+" = 5";
                Cursor cursor = db.rawQuery(sql,null);
                if(cursor != null){
                    while(cursor.moveToNext()){
                        int id = cursor.getInt(cursor.getColumnIndex("id"));
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        int age = cursor.getInt(cursor.getColumnIndex("age"));
                        Log.i("MainActivity","person id is "+id);
                        Log.i("MainActivity","person name is "+name);
                        Log.i("MainActivity","person age is "+age);
                    }

第二种方法：使用android API封装好的修改数据的操作

public class MainActivity extends AppCompatActivity {
    private Button mSelectButton;
    private MySqliteHelper mMySqliteHelper;
    private SQLiteDatabase db;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mMySqliteHelper = DbManger.getIntance(MainActivity.this);
        mSelectButton = (Button) findViewById(R.id.select_btn);
        //点击按钮查询数据
        mSelectButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                db = mMySqliteHelper.getWritableDatabase();
                Cursor cursor = db.query(Constant.TABLE_NAME,null,"id = ?",new String[]{"5"},
                null,null,null);
                if(cursor != null){
                    while(cursor.moveToNext()){
                        int id = cursor.getInt(cursor.getColumnIndex("id"));
                        String name = cursor.getString(cursor.getColumnIndex("name"));
                        int age = cursor.getInt(cursor.getColumnIndex("age"));
                        Log.i("MainActivity","person id is "+id);
                        Log.i("MainActivity","person name is "+name);
                        Log.i("MainActivity","person age is "+age);
                    }
                }
                cursor.close();
                db.close();
            }
        });
    }
}