Function PlanCacheComputeResultDesc

src/backend/utils/cache/plancache.c:2019–2046

* PlanCacheComputeResultDesc: given a list of analyzed-and-rewritten Queries, * determine the result tupledesc it will produce. Returns NULL if the * execution will not return tuples. * * Note: the result is created or copied into current memory context. */

 * Note: the result is created or copied into current memory context.
 */
static TupleDesc
PlanCacheComputeResultDesc(List *stmt_list)
{
	Query	   *query;

	switch (ChoosePortalStrategy(stmt_list))
	{
		case PORTAL_ONE_SELECT:
		case PORTAL_ONE_MOD_WITH:
			query = linitial_node(Query, stmt_list);
			return ExecCleanTypeFromTL(query->targetList);

		case PORTAL_ONE_RETURNING:
			query = QueryListGetPrimaryStmt(stmt_list);
			Assert(query->returningList);
			return ExecCleanTypeFromTL(query->returningList);

		case PORTAL_UTIL_SELECT:
			query = linitial_node(Query, stmt_list);
			Assert(query->utilityStmt);
			return UtilityTupleDescriptor(query->utilityStmt);

		case PORTAL_MULTI_QUERY:
			/* will not return tuples */
			break;
	}
	return NULL;
}

/*
 * PlanCacheRelCallback