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  3. Introduction to Relational Databases in SQL

Exercise

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.

Instructions 1/2

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  • 1

    Add a unique constraint to the university_shortname column in universities. Give it the name university_shortname_unq.

  • 2

    Add a unique constraint to the organization column in organizations. Give it the name organization_unq.