Simple SQL query problem

Question

Hi,
I'm trying create a simple query which tells me the occurance of a particular football match on a particular date. The table is as follows...
CREATE TABLE match
(matchId NUMBER(5)
CONSTRAINT match_matchId_nn NOT NULL,
matchDate DATE
CONSTRAINT match_date_nn NOT NULL,
stadiumId          NUMBER(5)
CONSTRAINT match_stadiumId_nn NOT NULL,
CONSTRAINT matchId_pk PRIMARY KEY (matchId));
Bascially, i'm trying to create a trigger which will implement the constraint that 'only one match can be at one stadium on a particular date'.
Any ideas guys?
Cheers...

Answer 1

ALTER TABLE match ADD CONSTRAINT match_date_uk UNIQUE
(stadiumId, matchDate)Bear in mind, though, that using dates in unique constraints can be problematic, because of the time element, which means there are 86400 unique values for each day. If your application enforces a rule that has only one match per stadium per day then all you need is a TRUNC() call in an insert/update trigger to make sure of that. If your application is going to allow more than one match per day the checking logic starts to get messy...
Cheers, APC
P.S. Oleg's solution is incorrect because it includes the primary key MatchId, which would thus permit duplicate combinations of stadium and date.