2 Primary keys in a PostgreSQL table?

Question

I have been given an ERD of a database that I need to create in PostgreSQL. Shown below.

As you can see on the table Enroll, there are two primary keys that are also foreign keys as well that need to be in that table, how would I go about creating this table this is what I have so far,

create table enroll( 
 class_code varchar(15) primary key references class(class_code), 
 trn_num int primary key references TRAINEE(trn_num), 
 enroll_date date, 
 enroll_grade int
);

Many thanks in advance for any help!

This sounds like homework, but here's a hint - there's not two primary keys, there's one primary key consisting of two columns. — Eric Petroelje
– Eric Petroelje, Commented Jan 24, 2019 at 14:39
University work, brilliant, I think I know what you are talking about! Cheers for the help! @EricPetroelje — Antonio
– Antonio, Commented Jan 24, 2019 at 14:41

Antonio · Accepted Answer · 2019-01-24 15:01:34Z

5

Answer: Create a composite primary key.

create table enroll( 
   class_code varchar(15) references class(class_code), 
   trn_num int  references TRAINEE(trn_num),
   enroll_date date, 
   enroll_grade int,
   primary key(class_code, trn_num)

);

answered Jan 24, 2019 at 15:01

Antonio

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