小编Ion*_*n C的帖子

我有一个活动片段,上面有一个listview元素.无法将数据添加到listview.谁能告诉我有什么问题？

public class MainActivity extends FragmentActivity {

    public String[] listS ={"item1","item2","item3"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main); 
        FragmentManager fm = getSupportFragmentManager();
        FragmentTransaction ft = fm.beginTransaction();
        MainFragment f = new MainFragment();
        ft.replace(R.id.fragcontainer, f);
        ft.commit();    
        //here the problem occurs
        ListView lv = (ListView)findViewById(R.id.listf);
        lv.setAdapter(new ArrayAdapter<String>(this, R.layout.list_row,R.id.labeld, listS));
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}

片段的类:

public class MainFragment extends …

我有一个简单的SQL查询:

SELECT  
       columnA, columnB, columnC...  
 FROM  
       (SELECT    
             columnA, columnB, columnC...  
        FROM   
              SomeTable) Table1  
  WHERE NOT EXISTS  
        (SELECT   
               columnA  
          FROM  
               SomeOtherTable st  
          WHERE  
               st.columnB = Table1.columnB)

任何人都可以给我一个建议如何重写此查询以获得更好的性能？我的意思是WHERE NOT EXISTS在表1中包含该子句.

我需要提高此查询的性能：

Select 
   t1.column1, t1.column2 
From
   table1 t1, table2 t2
Where 
   t1.id = t2.id and
   t1.some_column = t2.some_column
--------
minus
--------
Select 
   t1.column1, t1.column2 
From
   table1 t1, table2 t2, table3 t3
Where 
   t1.id = t2.id and
   t1.some_column = t2.some_column and
   t1.id = t3.id

我正在尝试使用“不存在”而不是“减号”重写此查询。有人可以给我建议吗？