code is 

when_button_pressed trigger.

declare
	 fdcode dmas.dcode%type;
	 fcodno dmas.codno%type;
	 famtrs dmas.amtrs%type;
	 fdate donres.rdate%type;
	 begin
	select dcode,codno,amtrs into fdcode,fcodno,famtrs  from dmas where descr=:BLOCK10.FOODTYPE;
	select rdate into fdate from donres;
	loop 
		CASE fdcode
	WHEN 'f' then 
		if  fdate = :BLOCK10.REDATE  AND (fdcode = 'f' or fdcode='b' or fdcode='l' or fdcode='d' or fcodno='s') then
			message( 'FOOD ALREADY BOOKED');
		ELSE
			:BLOCK10.AMOUNT := famtrs;
			exit;
		end if;
		when 'b' then
			 if fdate=:BLOCK10.REDATE AND (fdcode ='f' or fcodno='b') then
			 		message( 'FOOD ALREADY BOOKED');
			 else
			 	:BLOCK10.AMOUNT := famtrs;
			 	exit;	
			 end if;
		when 'l' then
			 if fdate =:BLOCK10.REDATE AND (fdcode='f' or fcodno='l') then
			 	message( 'FOOD ALREADY BOOKED');
			 else
			 	:BLOCK10.AMOUNT := famtrs;
			 	exit;
			 end if;
		 when 'd' then
			 if fdate =:BLOCK10.REDATE AND (fdcode='f' or fcodno='d') then
			 	message( 'FOOD ALREADY BOOKED');
			 else
			 	:BLOCK10.AMOUNT := famtrs;
			 	exit;
			 end if;
		 when 's' then 	 
			 if fdate=:BLOCK10.REDATE AND (fdcode='f' or fcodno='s') then
			 	message( 'FOOD ALREADY BOOKED');
			 else
			 	:BLOCK10.AMOUNT := famtrs;
			 	exit;
			 end if;
	end case;
	 end loop;
exception
	when too_many_rows then
	message('error too many ');
		end;

	select rdate into fdate from donres;
	loop