Trigger problems in PLSQL - oracle

Question

I've been trying to get a trigger that will essentially run a constraint like this;
CONSTRAINT (Date <= Meeting.EndDate)
Where it will compare the Date stated in one table (Race) with the Date stated in another table (Meeting). I know I could achieve this using foreign keys but I'm pretty sure to get more marks I need to use a trigger.
So far I've got this:
CREATE OR REPLACE TRIGGER race_date_trg
AFTER INSERT OR UPDATE
ON RACE
FOR EACH ROW
DECLARE
MEETING_ENDDATE DATE;
STARTDATE race.racedate%TYPE;
BEGIN
SELECT ENDDATE INTO MEETING_ENDDATE FROM meeting;
IF STARTDATE > MEETING_ENDDATE THEN
RAISE_APPLICATION_ERROR(-20000, 'Wrong start date!');
END IF;
end race_date_trg;
It compiles fine, but when I try and populate my tables with something that will raise the error, I'm getting this:
Error report:
SQL Error: ORA-04091: table SE488.MEETING is mutating, trigger/function may not see it
ORA-06512: at "SE488.RACE_DATE_TRG", line 5
ORA-04088: error during execution of trigger 'SE488.RACE_DATE_TRG'
04091. 00000 - "table %s.%s is mutating, trigger/function may not see it"
*Cause: A trigger (or a user defined plsql function that is referenced in
this statement) attempted to look at (or modify) a table that was
in the middle of being modified by the statement which fired it.
*Action: Rewrite the trigger (or function) so it does not read that table.
Thanks for the help.
Creation of the tables:
CREATE TABLE Meeting
(
MeetLocation varchar2(60),
StartDate date,
EndDate date,
MeetName varchar2(60)
);
CREATE TABLE Race
(
RaceID NUMBER,
RaceLocation varchar2(60),
MeetingStart date,
RaceDate date,
RaceTime timestamp(0),
RaceName varchar2(60),
RaceType varchar2(8),
MinAge numeric(2),
MaxAge numeric(2),
Sex varchar2(2) NULL
);
Populating them:
INTO Meeting (MeetLocation,StartDate,EndDate,MeetName)
values('Talbot','30-Jul-05','07-Aug-05','Midlands Derby')
INTO Meeting (MeetLocation,StartDate,EndDate,MeetName)
values('Ascot','04-Jul-10','07-Aug-10','National Derby')
INTO Race (RaceID,RaceLocation,MeetingStart,RaceDate,RaceTime,RaceName,RaceType,MinAge,MaxAge,Sex)
values('1','Talbot','20-Jul-05','31-Jul-05',to_date('2005/07/31:12:00:00PM', 'yyyy/mm/dd:hh:mi:sspm'),'600m Dash','Flat','2','10','M')
INTO Race (RaceID,RaceLocation,MeetingStart,RaceDate,RaceTime,RaceName,RaceType,MinAge,MaxAge,Sex)
values('2','Talbot','30-Jul-05','01-Aug-05',to_date('2005/08/01:01:10:00PM', 'yyyy/mm/dd:hh:mi:sspm'),'1km Hurdles','Flat','6','12','F')

Answer 1

CREATE OR REPLACE TRIGGER race_date_trg
BEFORE INSERT OR UPDATE ON RACE
FOR EACH ROW
DECLARE
meet_date date;
start_date date := :new.RaceDate;
BEGIN
SELECT StartDate INTO meet_date FROM meeting WHERE MeetLocation = :new.RaceLocation;
IF start_date > meet_date THEN
RAISE_APPLICATION_ERROR(-20000, 'Wrong start date!');
END IF;
END race_date_trg;
/
I Think you want raise error or exception. When someone insert or update table race, If start date (from table race) is lower than meet date (from table meeting).
:D