MigrateSQLMap how to instantiate if table has no primary key
To migrate content into Drupal taxonomy terms, use the MigrateDestinationTerm class, not MigrateDestinationTable. Here is example code

    $this-&gt;map = new MigrateSQLMap(
      $this-&gt;machineName,
      array(
        'term_id' =&gt; array(
          'type' =&gt; 'int',
          'not null' =&gt; TRUE,
          'description' =&gt; 'Term ID',
        ),
      ),
      MigrateDestinationTerm::getKeySchema()
    );