title: Postgres: How to do Composite keys?
body: <p>I cannot understand the syntax error in creating a composite key. It may be a logic error, because I have tested many varieties.</p>
  
  <p><strong>How do you create composite keys in Postgres?</strong></p>
  
  <pre><code>CREATE TABLE tags
       (
                (question_id, tag_id) NOT NULL,
                question_id INTEGER NOT NULL,
                tag_id SERIAL NOT NULL,
                tag1 VARCHAR(20),
                tag2 VARCHAR(20),
                tag3 VARCHAR(20),
                PRIMARY KEY(question_id, tag_id),
                CONSTRAINT no_duplicate_tag UNIQUE (question_id, tag_id)
       );
      ERROR:  syntax error at or near "("
      LINE 3:               (question_id, tag_id) NOT NULL,
                            ^
  </code></pre>