我想在我的android数据库中搜索重复的用户名

usrname是在edittext中输入的字符串，username是数据库中已经存在的字符串

Cursor c=db.rawQuery("Select orders from table_name where usrname=username;",null);

改变条件

if(c!=null)
{
    Toast.makeText(this,"Username already exists,please use a different username",Toast.LENGTH_SHORT).show();
}

---

在聊天时请注意导师

   if(c.getCount()>0) { 
Toast.makeText(this,"Username already exists,please use a different username",Toast.LENGTH_SHORT).show();
 }

Cursor c=db.rawQuery("Select orders from table_name where usrname=yourusername",null);
if(c.getcount>0)
{
    Toast.makeText(this,"Username already exists,please use a different username",Toast.LENGTH_SHORT).show();
}