Is it possible to have JavaScript code in the PL/SQL block?

• YES

But, what you're trying to do wont work which is passing javascript function AFTER SUBMIT.It'll only work if you change the point of execution to AFTER HEADER.

Alternatively, if you just want to validate the values entered and doesn't want to use apex validation, you can use APEX_ERROR package.Try this.

DECLARE

  v_count   NUMBER;



  BEGIN

        select prd_items into v_count

        from summary

        where prd_items = 'Total';

        -- I dont really know what you want to 

        --accomplish with this query but Im pretty sure 

        --It will not return a number

        -- if you want to count the number of prd_items it should be like this

        --select COUNT(*) 

        --into v_count

        --from summary

        --where prd_items = 'Total';





    APEX_ERROR.ADD_ERROR(

      p_message            => 'The value of Total for BU is '||v_count||'.<br>'||

                              'You have to enter correct values to proceed further',

      p_display_location   => apex_error.c_inline_in_notification 

    );  



END; 

EDIT: if you want to show the error if count not equal to 100 then do something like this:

DECLARE

  v_count   NUMBER;



  BEGIN



     Select COUNT(*) 

     into v_count

     from summary

     where prd_items = 'Total';



  IF v_count != 100 THEN

    APEX_ERROR.ADD_ERROR(

      p_message            => 'The value of Total for BU is '||v_count||'.<br>'||

                              'You have to enter correct values to proceed further',

      p_display_location   => apex_error.c_inline_in_notification 

    );  





 END IF;

END;