Function ExpandRowReference

src/backend/parser/parse_target.c:1417–1499

* ExpandRowReference() * Transforms foo.* into a list of expressions or targetlist entries. * * This handles the case where foo is an arbitrary expression of composite * type. */

 * type.
 */
static List *
ExpandRowReference(ParseState *pstate, Node *expr,
				   bool make_target_entry)
{
	List	   *result = NIL;
	TupleDesc	tupleDesc;
	int			numAttrs;
	int			i;

	/*
	 * If the rowtype expression is a whole-row Var, we can expand the fields
	 * as simple Vars.  Note: if the RTE is a relation, this case leaves us
	 * with the RTE's selectedCols bitmap showing the whole row as needing
	 * select permission, as well as the individual columns.  However, we can
	 * only get here for weird notations like (table.*).*, so it's not worth
	 * trying to clean up --- arguably, the permissions marking is correct
	 * anyway for such cases.
	 */
	if (IsA(expr, Var) &&
		((Var *) expr)->varattno == InvalidAttrNumber)
	{
		Var		   *var = (Var *) expr;
		ParseNamespaceItem *nsitem;

		nsitem = GetNSItemByRangeTablePosn(pstate, var->varno, var->varlevelsup);
		return ExpandSingleTable(pstate, nsitem, var->varlevelsup, var->location, make_target_entry);
	}

	/*
	 * Otherwise we have to do it the hard way.  Our current implementation is
	 * to generate multiple copies of the expression and do FieldSelects.
	 * (This can be pretty inefficient if the expression involves nontrivial
	 * computation :-(.)
	 *
	 * Verify it's a composite type, and get the tupdesc.
	 * get_expr_result_tupdesc() handles this conveniently.
	 *
	 * If it's a Var of type RECORD, we have to work even harder: we have to
	 * find what the Var refers to, and pass that to get_expr_result_tupdesc.
	 * That task is handled by expandRecordVariable().
	 */
	if (IsA(expr, Var) &&
		((Var *) expr)->vartype == RECORDOID)
		tupleDesc = expandRecordVariable(pstate, (Var *) expr, 0);
	else
		tupleDesc = get_expr_result_tupdesc(expr, false);
	Assert(tupleDesc);

	/* Generate a list of references to the individual fields */
	numAttrs = tupleDesc->natts;
	for (i = 0; i < numAttrs; i++)
	{
		Form_pg_attribute att = TupleDescAttr(tupleDesc, i);
		FieldSelect *fselect;

		if (att->attisdropped)
			continue;