Question

I have the following problem:

I am trying to add every student in the Comp. Sci. department into a course, here are the DDL for the relations:

The desired course has values of (‘CS-001’, ‘Weekly Seminar’, ‘Comp. Sci.’, 0)

---

Department 
      (dept_name [primary key], building, budget)

Course 
      (course_id [primary key], title, dept_name, credits)

Instructor 
      (ID [primary key], name, dept_name, salary) 
      Foreign Key is dept_name references Department

Section
      (course_id [primary key], sec_id [primary key], semester [primary key], year [primary key], building, room_number, time_slot_id) 
      Foreign Key course_id references Course

Teaches 
      ( ID [primary key], course_id [primary key], sec_id [primary key], semester [primary key], year [primary key]) 
       Foreign key ID references Instructor,
Foreign Key (course_id,sec_id,semester,year) references Section

Takes 
      (ID [primary key], course_id [primary key], sec_id [primary key], semester [primary key], year [primary key], grade) 
      Foreign key(course_id,sec_id,semester,year) references section Foreign key(ID) references student

Student 
      (ID [primary key], name, dept_name, tot_cred) Foreign key(dept_name) references department

The problem is that I’m getting an error when trying to use an update statement (Error is 1241 Operand should have 1 column), correct my syntax as it is more than likely the problem:

update takes
set ID=ID, course_id='CS-001', sec_id='1', semester='Fall', year=2009, grade=null
where
(
select distinct name, ID
from student natural join takes
where dept_name='Comp. Sci.'
);

Sorry I’m new at MySQL, if you could just guide me to correcting my syntax and possibly a better solution than mine (not sure if mine is even a solution).

Answer 1

You have not specified a column in you WHERE clause that’s is why you are getting Error 1241 Operand should contain 1 column(s)

update takes
set ID=ID, course_id='CS-001', sec_id='1', semester='Fall', year=2009, grade=null
where
(
   select distinct name, ID
   from student natural join takes
   where dept_name='Comp. Sci.'
);

Alternatively, join both tables

UPDATE  takes a 
        INNER JOIN student b
            ON a.ID = b.ID 
SET     a.ID = ID, 
        a.course_id='CS-001', 
        a.sec_id='1', 
        a.semester='Fall', 
        a.`year` = 2009, 
        a.grade = 0        -- you can't set NULL value when updating a column
WHERE   b.dept_name = 'Comp. Sci.'