Make your columns UNIQUE with ADD CONSTRAINT

As seen in the video, you add the UNIQUE keyword after the column_name that should be unique. This, of course, only works for new tables:

CREATE TABLE table_name (
 column_name UNIQUE
);

If you want to add a unique constraint to an existing table, you do it like that:

ALTER TABLE table_name
ADD CONSTRAINT some_name UNIQUE(column_name);

Note that this is different from the ALTER COLUMN syntax for the not-null constraint. Also, you have to give the constraint a name some_name.

Latihan ini adalah bagian dari kursus

Introduction to Relational Databases in SQL

Cobalah latihan ini dengan menyelesaikan kode contoh berikut.

-- Make universities.university_shortname unique
ALTER ___ ___
ADD ___ ___ UNIQUE(___);