PostgreSQL ERROR: syntax error at or near "varchar"

Question

I'm trying to alter the course_id column in the table 'course' but I keep getting this error:

CREATE TABLE course 
(
 course_id varchar(10) PRIMARY KEY, 
 title varchar(30), 
 dep_name varchar(10), 
 credits numeric(2,2) CHECK (credits>0)
);

ALTER TABLE takes ALTER COLUMN course_id varchar(10) REFERENCES course(course_id);

ERROR: syntax error at or near "varchar" LINE 1: ALTER TABLE takes ALTER COLUMN course_id varchar(10) REFEREN...

Answer 1

Altering a column's type and adding a foreign key on it are two different statements:

ALTER TABLE takes ALTER COLUMN course_id TYPE VARCHAR(10);

ALTER TABLE takes 
ADD CONSTRAINT takes_course_fk FOREIGN KEY (course_id) 
REFERENCES course(course_id);

Answer 2

Your syntax is worng. It must be:

ALTER TABLE takes ALTER COLUMN course_id TYPE varchar(10) ;