我正在尝试比较两个数据库并获取其他数据库中不存在的所有用户。对于例如数据库wp_members有正确的成员列表和数据库成员缺少一些成员然后我想比较wp_members和成员用户名，并找出成员中缺少的用户名，以便我可以添加它们。 （应选择wp_members用户名）
这是db
的SQL小提琴http://sqlfiddle.com/#!9/6a795e
这就是我想要做的事情
SELECT m.username FROM wp_members m, member n WHERE m.username<>n.username and n.siteid=1 group by m.username
但没有成功。
答案 0 :(得分：0)
可以通过public class MainActivity extends AppCompatActivity {
public static Bundle myBundl = new Bundle();
private List<ItemSlideMenu> listSliding;
private SlidingMenuAdapter3 adapter;
private Calendar calendar;
private TextView dateView;
TimePicker timePicker2;
final Context context = this ;
private int year, month, day;
private ListView listViewSliding;
private DrawerLayout drawerLayout;
private ActionBarDrawerToggle actionBarDrawerToggle;
String name1;
@RequiresApi(api = Build.VERSION_CODES.N)
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
calendar = Calendar.getInstance();
year = calendar.get(Calendar.YEAR);
month = calendar.get(Calendar.MONTH);
day = calendar.get(Calendar.DAY_OF_MONTH);
showDate(year, month+1, day);
//Init component
listViewSliding = (ListView) findViewById(R.id.lv_sliding_menu);
drawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
listSliding = new ArrayList<>();
//Add item for sliding list
listSliding.add(new ItemSlideMenu(R.drawable.home_96,"Accueil" ));
listSliding.add(new ItemSlideMenu(R.drawable.cocktail,"Organiser une Sortie"));
listSliding.add(new ItemSlideMenu(R.drawable.geo,"Autour de moi"));
listSliding.add(new ItemSlideMenu(R.drawable.ami,"Liste d'amis" ));
listSliding.add(new ItemSlideMenu(R.drawable.message,"Contact"));
listSliding.add(new ItemSlideMenu(R.drawable.information,"Credits"));
adapter = new SlidingMenuAdapter3(this, listSliding);
listViewSliding.setAdapter(adapter);
//Display icon to open/ close sliding list
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
//Set title
setTitle(listSliding.get(0).getTitle());
//item selected
listViewSliding.setItemChecked(0, true);
//Close menu
drawerLayout.closeDrawer(listViewSliding);
//Display fragment 1 when start
replaceFragment(0);
//Hanlde on item click
listViewSliding.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
//Set title
setTitle(listSliding.get(position).getTitle());
//item selected
listViewSliding.setItemChecked(position, true);
if (position==2){
Intent i2 = new Intent(getApplicationContext(), MapsActivity.class);
startActivity(i2);
} else
{//Replace fragment
replaceFragment(position);
}//Close menu
drawerLayout.closeDrawer(listViewSliding);
}
});
actionBarDrawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.drawer_opened, R.string.drawer_closed){
@Override
public void onDrawerOpened(View drawerView) {
super.onDrawerOpened(drawerView);
invalidateOptionsMenu();
}
@Override
public void onDrawerClosed(View drawerView) {
super.onDrawerClosed(drawerView);
invalidateOptionsMenu();
}
};
drawerLayout.setDrawerListener(actionBarDrawerToggle);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if(actionBarDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
actionBarDrawerToggle.syncState();
}
//Create method replace fragment
private void replaceFragment(int pos) {
android.support.v4.app.Fragment fragment = null;
switch (pos) {
case 0:
fragment = new Fragment1();
break;
case 1:
fragment = new Fragment2();
break;
case 2:
fragment = new Fragment3();
break;
case 3 :
fragment = new Fragment4();
break;
}
if(null!=fragment) {
android.support.v4.app.FragmentManager fragmentManager = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.main_content,fragment);
transaction.addToBackStack(null);
transaction.commit();
}
}
@SuppressWarnings("deprecation")
protected Dialog onCreateDialog(int id) {
// TODO Auto-generated method stub
if (id == 999) {
return new DatePickerDialog(this,
myDateListener, year, month, day);
}
else if (id ==98) {
final Dialog dialog = new Dialog(context);
dialog.setContentView(R.layout.custom);
dialog.setTitle("Title...");
// set the custom dialog components - text, image and button
Button dialogButton = (Button) dialog.findViewById(R.id.dialogButtonOK);
dialogButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Fragment6 fragment = null;
fragment = new Fragment6();
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.contact, fragment);
transaction.addToBackStack(null);
transaction.commit();
dialog.dismiss();
}
});
dialog.show();
// if button is clicked, close the custom dialog
}
return null;
}
private DatePickerDialog.OnDateSetListener myDateListener = new
DatePickerDialog.OnDateSetListener() {
@Override
public void onDateSet(DatePicker arg0,
int arg1, int arg2, int arg3) {
// TODO Auto-generated method stub
// arg1 = year
// arg2 = month
// arg3 = day
showDate(arg1, arg2+1, arg3);
}
};
private void showDate(int year, int month, int day) {
StringBuilder abbes = new StringBuilder().append(day).append("/")
.append(month).append("/").append(year);
Bundle bundle = new Bundle();
bundle.putString("edttext", String.valueOf(abbes));
// set Fragmentclass Arguments
Fragment5 fragobj = new Fragment5();
fragobj.setArguments(bundle);
}
表格和搜索LEFT JOIN条目来找到此问题的一般解决方案。
NULL答案 1 :(得分：0)
使用内部联接无法解决此问题。内部联接只能对符合条件的行进行，而不是在没有＆＃39; no＆＃39;匹配。
您可以对两个表执行左外连接并在用户名上进行匹配，然后在WHERE子句中筛选出具有n.username的NULL值的结果。
SELECT m.username FROM wp_members m LEFT OUTER JOIN members n ON m.username = n.username AND n.siteid = 1 WHERE n.username IS NULL GROUP BY m.username;
另一种方法是使用带有子查询的NOT IN语句。
SELECT m.username FROM wp_members m WHERE m.username NOT IN (SELECT n.username FROM members n AND n.siteid = 1) GROUP BY m.username;
使用外连接的解决方案会更快，但可能不那么重要。