Use trigger as assertion in MySQL - mysql

Question

I have a database and a few tables in MySql. I am trying to implement an Oracle assertion in MySQL using CREATE TRIGGER. I am not sure if I used the proper syntax.
This is what I have so far, but I'm not sure why it's wrong.
CREATE TRIGGER tg_review_before_insert
BEFORE INSERT ON review
FOR EACH ROW
SET NEW.paper = IF((SELECT * FROM paper P WHERE 3 <>(SELECT COUNT(*)
FROM review R
WHERE R.paperid = P.paperid)
);
Here are my tables:
CREATE TABLE paper(
paperid INT UNSIGNED NOT NULL AUTO_INCREMENT,
title VARCHAR(50) NOT NULL,
abstract VARCHAR(250),
pdf VARCHAR(100),
PRIMARY KEY(paperid)
);
CREATE TABLE author(
email VARCHAR(100) NOT NULL,
name VARCHAR(50),
affiliation VARCHAR(100),
PRIMARY KEY(email)
);
CREATE TABLE writePaper(
paperid INT UNSIGNED NOT NULL AUTO_INCREMENT,
email VARCHAR(100),
paper_order INT,
PRIMARY KEY(paperid, email),
FOREIGN KEY(paperid) REFERENCES paper(paperid),
FOREIGN KEY(email) REFERENCES author(email)
);
CREATE TABLE pcmember(
email VARCHAR(100) NOT NULL,
name VARCHAR(20),
PRIMARY KEY(email)
);
CREATE TABLE review(
reportid INT UNSIGNED,
sdate DATE,
comment VARCHAR(250),
recommendation CHAR(1),
paperid INT UNSIGNED,
email VARCHAR(100),
PRIMARY KEY(paperid, email),
FOREIGN KEY(paperid) REFERENCES paper(paperid),
FOREIGN KEY(email) REFERENCES pcmember(email)
);
Here are the assertions I am trying to implement from Oracle SQL code to MySQL SQL code:
CREATE ASSERTION assert
CHECK NOT EXISTS(SELECT * FROM paper P WHERE 3 <>(SELECT COUNT(*)
FROM review R
WHERE R.paperid = P.paperid)
);
CREATE ASSERTION atmostfivepapers
CHECK NOT EXISTS(SELECT * FROM pcmember P WHERE 5 <
( SELECT *
FROM review R
WHERE R.email = P.email
)
);