title: PostgreSQL C aggregate function: How to return multiple values in transition function
body: <p>I'm writing a C aggregate function in PostgreSQL, currently I use bytea as transition type and my_transfunc returns only one bytea data and everything works OK:</p>
  
  <pre><code>Datum my_transfunc(PG_FUNCTION_ARGS) {
          bytea *trans_value = PG_GETARG_BYTEA_P(0);
          .........
  }
  
  Data my_finalfunc(PG_FUNCTION_ARGS) {
          bytea *trans_value = PG_GETARG_BYTEA_P(0);
          .........
  }
  </code></pre>
  
  <p>However now, at my_finalfunc, apart from bytea, I need one more variable from my_transfunc which's type is oid.</p>
  
  <p>The question is how can I return one bytea and one oid in my_transfunc ?</p>