Question

I have created ‘students’ table where ‘sid’ is the primary key and I have inserted many values into sid. I have created a second table called ‘courses’ and it has a primary key ‘cid’ I have entered values for cid as well. Now, I want to create a relation table called ‘enroll’ which I have done like-

create table enroll(
    grade char(2),
    sid int not null,
    cid int not null,
    primary key(sid,cid),
    foreign key (cid) references courses(cid) on delete cascade,
    foreign key (sid) references students(sid) on delete cascade
);

Now, when I try to view the table using select * from enroll;
I don’t get any output. It says “0 rows returned”. Why is this? Isn’t it supposed to have all the values of sid and cid from the other tables?

Answer 1

In Order to create a new table from values in your other table you can do something like this:

CREATE TABLE new_table AS (SELECT * FROM old_table);

• The select statement will be the fields that will be pulled.
• You can rename the columns like: Select [field name] as [what you want field name to be]

For More information read this article

Anyway for your particular case:

 Create table enroll AS (Select s.sid AS 'Sid', c.cid AS 'Cid' from courses c inner join students s on c.something = s.something)

replace ‘.something’ with the id of the student