在SQLyog中创建触发器时对DECLARE报错

在SQLyog中我使用如下代码创建触发器

报错如下

想请教一下如何解决

这是我构建的表

CREATE TABLE Student
    (Sno  CHAR(9),  
     Sname  CHAR(20) NOT NULL,
     Ssex  CHAR(2),
     Sage  SMALLINT,
     Sdept  CHAR(20),
     PRIMARY KEY (Sno)
     ); 
     
CREATE TABLE Course(
    Cno CHAR(9),
    Cname CHAR(20) NOT NULL,
    Cpno CHAR(9),
    Credit INT,
    PRIMARY KEY(Cno)
);
    
CREATE TABLE SC
     (  Sno    CHAR(9)  NOT NULL, 
        Cno     CHAR(4)  NOT NULL,  
        Grade    SMALLINT,
        PRIMARY KEY (Sno, Cno),   /*在表级定义实体完整性*/
        FOREIGN KEY (Sno) REFERENCES Student(Sno),  
              /*在表级定义参照完整性*/
        FOREIGN KEY (Cno) REFERENCES Course(Cno)    
              /*在表级定义参照完整性*/
      );


INSERT INTO Student
VALUES('201215121', '李勇', '男', 20, 'CS');
INSERT INTO Student
VALUES('201215122', '刘晨', '女', 19, 'CS');
INSERT INTO Student
VALUES('201215123', '王敏', '女', 18, 'MA');
INSERT INTO Student
VALUES('201215125', '张立', '男', 19, 'IS');

INSERT INTO Course
VALUES('1', '数据库', '5', 4); 
INSERT INTO Course
VALUES('2', '数学', NULL, 2); 
INSERT INTO Course
VALUES('3', '信息系统', '1', 4); 
INSERT INTO Course
VALUES('4', '操作系统', '6', 3); 
INSERT INTO Course
VALUES('5', '数据结构', '7', 4); 
INSERT INTO Course
VALUES('6', '数据处理', NULL, 2); 
INSERT INTO Course
VALUES('7', 'PASCAL语言', '6', 4); 

INSERT INTO SC
VALUES('201215121', '1', 92); 
INSERT INTO SC
VALUES('201215121', '2', 85); 
INSERT INTO SC
VALUES('201215121', '3', 88); 
INSERT INTO SC
VALUES('201215122', '2', 90);
INSERT INTO SC
VALUES('201215122', '3', 80);  


CREATE TABLE SC_U(
    Sno CHAR(9) PRIMARY KEY,
    Cno SMALLINT,
    OldGrade SMALLINT,
    NewGrade SMALLINT
);