Saving Checkbox data in a DB column

I created an item P1_checkbox in Oracle APEX, using LOV(select ename, empno from emp WHERE ename LIKE 's%';) which gives multiple checkboxes.
When I check the boxes, I want to INSERT the checked boxes data into another table "emp_selected".

Then, when I login into the application again, the application now should have the checkboxes ticked(checked) based on the data inserted into the table "emp_selected" along with unchecked boxes from table "emp" and when I uncheck some of pre-selected checkboxes and check the new checkboxes, it should be updated accordingly in "emp_selected".

My Oracle APEX version is 4.2.

An apex checkbox with multiple checkboxes will save its state as all selected values concatenated to eachother with a colon, eg One:Two:Three.
So you will have to seperate those values, loop over them, and save them.
And you will need to configure your checkbox source correctly.
See the sample page I set up (apex_demo/demo)

All my setup is on that page too. For the sake of the example I'm using an apex collection to simulate a table which stores the values. The principle is the exact same - you'll simple need to adapt to your table with your selections.

Checkboxes LOV SQL:

select ename, empno from emp

Checkboxes Source settings:

Source: Always - SQL Query return colon seperated value

select c001
from apex_collections
where collection_name = 'CHECKBOX_EXAMPLE'

This will take all the values selected and concatenate them to eachother with a colon. And the checkbox will take those values and mark them as being selected.

An after submit process:

DECLARE
    l_vc_arr2    APEX_APPLICATION_GLOBAL.VC_ARR2;
BEGIN
  apex_collection.create_or_truncate_collection('CHECKBOX_EXAMPLE');
    l_vc_arr2 := APEX_UTIL.STRING_TO_TABLE(:P37_CHECKBOXES);
    FOR z IN 1..l_vc_arr2.count LOOP
        apex_debug.message(l_vc_arr2(z));
        apex_collection.add_member(p_collection_name => 'CHECKBOX_EXAMPLE', p_c001 => l_vc_arr2(z));
    END LOOP;
END;