title: Primary key in "many-to-many" table
body: <p>I have a table in a SQL database that provides a "many-to-many" connection.</p>
  
  <p>The table contains id's of both tables and some fields with additional information about the connection. </p>
  
  <pre><code>CREATE TABLE SomeTable (
    f_id1 INTEGER NOT NULL,
    f_id2 INTEGER NOT NULL,
    additional_info text NOT NULL,
    ts timestamp NULL DEFAULT now()
  ); 
  </code></pre>
  
  <p>The table is expected to contain 10 000 - 100 000 entries.</p>
  
  <p>How is it better to design a primary key? Should I create an additional 'id' field, or to create a complex primary key from both id's?</p>
  
  <p>DBMS is PostgreSQL</p>