Oracle - Trigger [closed] - sql

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I am new to PL SQL. I have the following two tables: UserGame and Game.
CREATE TABLE Game (
GameID INT NOT NULL,
Name CHAR(100) NOT NULL,
Description CHAR(100) NOT NULL,
Publisher CHAR(100) NOT NULL,
AgeRating INT NOT NULL,
ImageLink CHAR(100),
WebsiteUrl CHAR(100),
AverageRating FLOAT,
OverallRanking INT,
CONSTRAINT pkGameId
PRIMARY KEY (GameID),
CONSTRAINT AgeRating CHECK (AgeRating >= 0),
CONSTRAINT OverallRankingMin CHECK (OverallRanking >= 0)
);
CREATE TABLE UserGame (
PlayerID INT NOT NULL,
GameID INT NOT NULL,
Rating INT,
RatingComment CHAR(100),
LastPlayed DATE,
HighestScore INT,
InProgress CHAR(1),
CONSTRAINT pkUserGame
PRIMARY KEY (PlayerID, GameID),
CONSTRAINT fkPlayerID
FOREIGN KEY (PlayerID)
REFERENCES Player (PlayerID),
CONSTRAINT fkGameIdTer
FOREIGN KEY (GameID)
REFERENCES Game (GameID),
CONSTRAINT RatingMin CHECK (Rating >= 0),
CONSTRAINT RatingMax CHECK (Rating <= 5),
CONSTRAINT HighestScore CHECK (HighestScore >= 0),
CONSTRAINT InProgress CHECK (InProgress IN (0,1))
);
I would like to update the average rating of a game, every time a player updates a rating in UserGame.
This is what I came up with.
CREATE OR REPLACE TRIGGER averageUpdate
AFTER UPDATE OF Rating ON UserGame
BEGIN
FOR r1 in (SELECT DISTINCT GameID FROM UserGame)
LOOP
UPDATE Game
SET Game.AverageRating = (SELECT AVG(Rating) FROM UserGame WHERE GameID = r1.GameID GROUP BY GameID)
WHERE Game.GameID = r1.GameID;
END LOOP;
END averageUpdate;
But it does not work and I get this error:
Error: ORA-00900: invalid SQL statement
SQLState: 42000
ErrorCode: 900
Error occured in:
END LOOP
Could anyone explain to me what I am doing wrong?
It seems the code I had posted was correct, as confirmed by Justin Cave. There must be something wrong with my set-up then.
To make sure of this, I ran the queries using SQL Fiddle, with success.

Answer 1

Are you sure that what you posted is actually what you're running? It works fine for me (once I remove the foreign keys to tables that you haven't provided).
SQL> CREATE TABLE Game (
2 GameID INT NOT NULL,
3 Name CHAR(100) NOT NULL,
4 Description CHAR(100) NOT NULL,
5 Publisher CHAR(100) NOT NULL,
6 AgeRating INT NOT NULL,
7 ImageLink CHAR(100),
8 WebsiteUrl CHAR(100),
9 AverageRating FLOAT,
10 OverallRanking INT,
11 CONSTRAINT pkGameId
12 PRIMARY KEY (GameID),
13 CONSTRAINT AgeRating CHECK (AgeRating >= 0),
14 CONSTRAINT OverallRankingMin CHECK (OverallRanking >= 0)
15 );
Table created.
SQL> ed
Wrote file afiedt.buf
1 CREATE TABLE UserGame (
2 PlayerID INT NOT NULL,
3 GameID INT NOT NULL,
4 Rating INT,
5 RatingComment CHAR(100),
6 LastPlayed DATE,
7 HighestScore INT,
8 InProgress CHAR(1),
9 CONSTRAINT fkGameIdTer
10 FOREIGN KEY (GameID)
11 REFERENCES Game (GameID),
12 CONSTRAINT RatingMin CHECK (Rating >= 0),
13 CONSTRAINT RatingMax CHECK (Rating <= 5),
14 CONSTRAINT HighestScore CHECK (HighestScore >= 0),
15 CONSTRAINT InProgress CHECK (InProgress IN (0,1))
16* )
SQL> /
Table created.
SQL> CREATE OR REPLACE TRIGGER averageUpdate
2 AFTER UPDATE OF Rating ON UserGame
3 BEGIN
4 FOR r1 in (SELECT DISTINCT GameID FROM UserGame)
5 LOOP
6 UPDATE Game
7 SET Game.AverageRating = (SELECT AVG(Rating) FROM UserGame WHERE GameID = r1.GameID GROUP BY GameID)
8 WHERE Game.GameID = r1.GameID;
9 END LOOP;
10 END averageUpdate;
11 /
Trigger created.
Can you cut and paste from a SQL*Plus session just as I did here showing exactly what you are doing?
This doesn't have any impact on your current question. But I would strongly suggest that you not use char(100) or float data types in this data model. All these strings are variable length so you should be using varchar2. char is a fixed-width data type. A char(100) will always store exactly 100 bytes of data. If your actual data is less than that, Oracle will add spaces at the end. If you try to search for a particular value in the table and you end up with char comparison semantics, you'll need to ensure that the search string is space-padded to 100 bytes. A varchar2 is a variable-width data type. It uses only as much space as is required for the actual data. It doesn't do pointless and wasteful space-padding of data. And you never need to worry about space-padding search strings.
I can also all but guarantee that you want your ratings to be number data types of some length and precision, not float. Floating point numbers are inherently imprecise so an game that might average a score of 4.4 might be represented in a float as 4.3999999999865 or 4.4000000000107 (making the numbers up). It's very unlikely that is the sort of score that your users want to see. If you use a number(4,3), you'll get 3 decimal digits of precision and you won't have to deal with errors (or imprecision if you prefer) in the least significant bits of the data. A game that averages a score of 4.4 will have a value of 4.4 not something very very close to 4.4.
From a performance standpoint, I would strongly suggest that you not use a trigger to meet this requirement. Particularly not a trigger that recomputes the score for every game every time any game gets rated. That will not scale well and you will be spending gobs of time constantly recalculating scores. Assuming you need to store the computed score, you probably want it to be refreshed periodically not immediately when a rating is entered. If you do want to recompute the score every time a game is rated, only recompute the score for the game that was rated not for every game in the system.