问使用PL/SQL匿名块插入

EN

DECLARE
    create_student VARCHAR2(500) := 'CREATE TABLE student(stu_id CHAR(5),Lname VARCHAR2(10) NOT NULL,Fname VARCHAR2(10) NOT NULL,Mi VARCHAR(2),Sex CHAR(1),Major VARCHAR(10),Home_State VARCHAR(4),CONSTRAINT stu_id_pk PRIMARY KEY (stu_id))';
    create_course VARCHAR(500) := 'CREATE TABLE course(course_id VARCHAR(8),section CHAR(3)NOT NULL,c_name VARCHAR(30)NOT NULL,c_description VARCHAR(50),CONSTRAINT course_id_pk PRIMARY KEY (course_id))';
    create_student_course VARCHAR(300) := 'CREATE TABLE student_course(stu_id CHAR(5),course_id VARCHAR(8),section CHAR(3),CONSTRAINT ck_stuid_courseid PRIMARY KEY (stu_id, course_id))';
    insert_student VARCHAR2(1200) := 'INSERT ALL
INTO student VALUES(‘10011’, ‘Smith’, ‘Peter’, ‘M’, ‘M’, ‘Math’, ‘TX’)
INTO student VALUES(‘10012’, ‘Jones’, ‘Sam’, ‘A’, ‘M’, ‘English’, ‘TX’)
INTO student VALUES(‘10013’, ‘Peters’, ‘Amy’, ‘A’, ‘F’, ‘English’, ‘ME’)
INTO student VALUES(‘10014’, ‘Johnson’, ‘John’, ‘J’, ‘M’, ‘CompSci’, ‘CA’)
INTO student VALUES(‘10015’, ‘Penders’, ‘Alton’, ‘P’, ‘F’, ‘Math’, ‘GA’)
INTO student VALUES(‘10016’, ‘Allen’, ‘Diane’, ‘J’, ‘F’, ‘Geography’, ‘Minn’)
INTO student VALUES(‘10017’, ‘Gill’, ‘Jennifer’, ‘‘, ‘F’, ‘CompSci’, ‘TX’)
INTO student VALUES(‘10018’, ‘Johns’, ‘Roberta’, ‘‘, ‘F’, ‘CompSci’, ‘TX’)
INTO student VALUES(‘10019’, ‘Wier’, ‘Paul’, ‘‘, ‘M’, ‘English’, ‘TX’)
SELECT * FROM dual';
BEGIN
    EXECUTE IMMEDIATE create_student;
    EXECUTE IMMEDIATE create_course;
    EXECUTE IMMEDIATE create_student_course;
    EXECUTE IMMEDIATE insert_student;
END;
/

Error report -
ORA-00955: name is already used by an existing object
ORA-06512: at line 17
00955. 00000 -  "name is already used by an existing object"
*Cause:    
*Action: