Try this :
Cursor c = mDb.rawQuery(
            "select * from table_name where column_name = ?",
            new String[] { "search" });
EDIT :
Follow the tutorial of the given above link and add below method into TestAdapter 
public Cursor get_tag_Data()
 {
     try
     {
         String sql ="select * from table_name where column_name = ?", new String[] { edittext.getText().toString().trim()}";
         Cursor mCur = mDb.rawQuery(sql, null);
         if (mCur!=null)
         {
            mCur.moveToNext();
         }
         return mCur;
     }
     catch (SQLException mSQLException) 
     {
         Log.e(TAG, "getTestData >>"+ mSQLException.toString());
         throw mSQLException;
     }
 }
and call this method from your class like:
 TestAdapter mDbHelper = new TestAdapter(urContext);        
 mDbHelper.createDatabase();      
mDbHelper.open();
Cursor testdata = mDbHelper.get_tag_Data();
mDbHelper.close();
EDIT: 
Declare below method into your database class,
 public List<String> getQuestions(String difficulty) {
   public static List<String> question_Set;
    question_Set = new ArrayList<String>();
    Cursor c = mDb.rawQuery(
            "select * from table_name where column_name = ?", new String[] { difficulty });
    while (c.moveToNext()) {
        question_Set.add(c.getString(1).trim());
    }
    return question_Set;
}
Now call like
DB.getQuestions(edittext.getText().toString().trim()); // DB is your database class name