sql table

CREATE TABLE classroom
    (building       VARCHAR(15),
     room_number        VARCHAR(7),
     capacity       NUMBER(4,0),
     PRIMARY KEY (building, room_number)
    );

CREATE TABLE department
    (dept_name      VARCHAR(20),
     building       VARCHAR(15),
     budget             NUMBER(12,2) CHECK (budget > 0),
     PRIMARY KEY (dept_name)
    );

CREATE TABLE course
    (course_id      VARCHAR(8),
     title          VARCHAR(50),
     dept_name      VARCHAR(20),
     credits        NUMBER(2,0) CHECK (credits > 0),
     PRIMARY KEY (course_id),
     FOREIGN KEY (dept_name) REFERENCES department
        ON DELETE SET NULL
    );

CREATE TABLE instructor
    (ID         VARCHAR(5),
     name           VARCHAR(20) NOT NULL,
     dept_name      VARCHAR(20),
     salary         NUMBER(8,2) CHECK (salary > 29000),
     PRIMARY KEY (ID),
     FOREIGN KEY (dept_name) REFERENCES department
        ON DELETE SET NULL
    );

CREATE TABLE SECTION
    (course_id      VARCHAR(8),
         sec_id         VARCHAR(8),
     semester       VARCHAR(6)
        CHECK (semester IN ('Fall', 'Winter', 'Spring', 'Summer')),
     YEAR           NUMBER(4,0) CHECK (YEAR > 1701 AND YEAR < 2100),
     building       VARCHAR(15),
     room_number        VARCHAR(7),
     time_slot_id       VARCHAR(4),
     PRIMARY KEY (course_id, sec_id, semester, YEAR),
     FOREIGN KEY (course_id) REFERENCES course
        ON DELETE cascade,
     FOREIGN KEY (building, room_number) REFERENCES classroom
        ON DELETE SET NULL
    );

CREATE TABLE teaches
    (ID         varchar2(5),
     course_id      varchar2(8),
     sec_id         varchar2(8),
     semester       varchar2(6),
     YEAR           NUMBER(4,0),
     CONSTRAINT "teaches_PK" PRIMARY KEY (ID, course_id, sec_id, semester, YEAR),
     CONSTRAINT "teaches_FK1" FOREIGN KEY (course_id,sec_id, semester, YEAR) REFERENCES SECTION
        ON DELETE cascade,
     CONSTRAINT "teaches_FK2" FOREIGN KEY (ID) REFERENCES instructor (ID)
        ON DELETE cascade
    );

CREATE TABLE student
    (ID         varchar2(5),
     name           varchar2(20) NOT NULL,
     dept_name      varchar2(20),
     tot_cred       NUMBER(3,0) CHECK (tot_cred >= 0),
     CONSTRAINT "student_PK" PRIMARY KEY (ID),
     CONSTRAINT "student_FK" FOREIGN KEY (dept_name) REFERENCES department
        ON DELETE SET NULL
    );

CREATE TABLE takes
    (ID         varchar2(5),
     course_id      varchar2(8),
     sec_id         varchar2(8),
     semester       varchar2(6),
     YEAR           NUMBER(4,0),
     grade              varchar2(2),
     CONSTRAINT "takes_PK" PRIMARY KEY (ID, course_id, sec_id, semester, YEAR),
     CONSTRAINT "takes_FK1" FOREIGN KEY (course_id,sec_id, semester, YEAR) REFERENCES SECTION
        ON DELETE cascade,
     CONSTRAINT "takes_FK2" FOREIGN KEY (ID) REFERENCES student
        ON DELETE cascade
    );

CREATE TABLE advisor
    (s_ID           varchar2(5),
     i_ID           varchar2(5),
     CONSTRAINT "advisor_PK" PRIMARY KEY (s_ID),
     CONSTRAINT "advisor_FK1" FOREIGN KEY (i_ID) REFERENCES instructor (ID)
        ON DELETE SET NULL,
     CONSTRAINT "advisor_FK2" FOREIGN KEY (s_ID) REFERENCES student (ID)
        ON DELETE cascade
    );

CREATE TABLE time_slot
    (time_slot_id       varchar2(4),
     DAY            varchar2(1),
     start_hr       NUMBER(2) CHECK (start_hr >= 0 AND start_hr < 24),
     start_min      NUMBER(2) CHECK (start_min >= 0 AND start_min < 60),
     end_hr         NUMBER(2) CHECK (end_hr >= 0 AND end_hr < 24),
     end_min        NUMBER(2) CHECK (end_min >= 0 AND end_min < 60),
     CONSTRAINT "time_slot_PK" PRIMARY KEY (time_slot_id, DAY, start_hr, start_min)
    );

CREATE TABLE prereq
    (course_id      varchar2(8),
     prereq_id      varchar2(8),
     PRIMARY KEY (course_id, prereq_id),
     FOREIGN KEY (course_id) REFERENCES course
        ON DELETE cascade,
     FOREIGN KEY (prereq_id) REFERENCES course
    );