Sqlite database with null objects in the database

Question

I trie to make an timetable. The problem is that I dont get passed the if(cursor.moveToFirst()) and every time it returns null. I want to set the strings in a TextView. My database: enter image description here

This is my databasehelper code:

` public String abcd() {

    sqLiteDatabase = this.getReadableDatabase();
    Cursor cursor = sqLiteDatabase.rawQuery("SELECT COLUMN_MONDAY FROM SCHEDULE_TABLE WHERE COLUMN_MONDAY = ? ", null);
    String getmonday = null;


    if(cursor.moveToFirst()) {
        do {

            getmonday = cursor.getString(cursor.getColumnIndex("COLUMN_MONDAY"));
            

        } while (cursor.moveToNext());
    }


    cursor.close();
    sqLiteDatabase.close();
    return getmonday;`

This is how I insert the data:

            try {
                //Checken welches Item beim spinnerDay ausgewählt ist und dann in die Datenbank einfügen

                if(spinnerDay.getSelectedItem().equals("Monday")) {
                    scheduleClass = new ScheduleClass(et_Subject.getText().toString(), null, null, null, null, null, null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else if(spinnerDay.getSelectedItem().equals("Tuesday")){
                    scheduleClass = new ScheduleClass(null, et_Subject.getText().toString(), null, null, null, null, null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else if(spinnerDay.getSelectedItem().equals("Wednesday")){
                    scheduleClass = new ScheduleClass(null, null, et_Subject.getText().toString(), null, null, null, null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else if(spinnerDay.getSelectedItem().equals("Thursday")){
                    scheduleClass = new ScheduleClass(null, null, null, et_Subject.getText().toString(), null, null, null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else if(spinnerDay.getSelectedItem().equals("Friday")){
                    scheduleClass = new ScheduleClass(null, null,null, null,  et_Subject.getText().toString(), null, null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else if(spinnerDay.getSelectedItem().equals("Saturday")){
                    scheduleClass = new ScheduleClass(null, null, null, null, null,  et_Subject.getText().toString(), null, Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }
                else {
                    scheduleClass = new ScheduleClass(null, null, null, null, null,  null, et_Subject.getText().toString(), Integer.parseInt(spinnerHour.getSelectedItem().toString()), Integer.parseInt(et_Room.getText().toString()), -1);
                    Toast.makeText(ScheduleEingebenActivity.this, scheduleClass.toString(), Toast.LENGTH_LONG).show();
                }


            }catch (Exception e) {
                Toast.makeText(ScheduleEingebenActivity.this, "Something went wrong", Toast.LENGTH_LONG).show();
                scheduleClass = new ScheduleClass(null, null, null, null, null, null, null,0, 0, -1);
            }

            ScheduleDatabaseHelper scheduleDatabaseHelper = new ScheduleDatabaseHelper(ScheduleEingebenActivity.this);

            boolean success = scheduleDatabaseHelper.addOne(scheduleClass);

            Toast.makeText(ScheduleEingebenActivity.this, "Success" + success, Toast.LENGTH_LONG).show();

Answer 1

? is a placeholder for which you must supply its value in the 2nd argument of rawQuery().

But if all you want is the non null values of the column COLUMN_MONDAY then there is no need to pass any parameter value.
Your sql statement can be written as:

SELECT COLUMN_MONDAY FROM SCHEDULE_TABLE WHERE COLUMN_MONDAY IS NOT NULL

So your java code should be:

Cursor cursor = sqLiteDatabase.rawQuery("SELECT COLUMN_MONDAY FROM SCHEDULE_TABLE WHERE COLUMN_MONDAY IS NOT NULL", null);

But this, most probably will return more than 1 rows, in which case it is not clear which value of all these rows should be returned.
The loop in your code will return the last value.