Function relationHasPrimaryKey

src/backend/catalog/index.c:167–198

* relationHasPrimaryKey * See whether an existing relation has a primary key. * * Caller must have suitable lock on the relation. * * Note: we intentionally do not check indisvalid here; that's because this * is used to enforce the rule that there can be only one indisprimary index, * and we want that to be true even if said index is invalid. */

 * and we want that to be true even if said index is invalid.
 */
bool
relationHasPrimaryKey(Relation rel)
{
	bool		result = false;
	List	   *indexoidlist;
	ListCell   *indexoidscan;

	/*
	 * Get the list of index OIDs for the table from the relcache, and look up
	 * each one in the pg_index syscache until we find one marked primary key
	 * (hopefully there isn't more than one such).
	 */
	indexoidlist = RelationGetIndexList(rel);

	foreach(indexoidscan, indexoidlist)
	{
		Oid			indexoid = lfirst_oid(indexoidscan);
		HeapTuple	indexTuple;

		indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
		if (!HeapTupleIsValid(indexTuple))	/* should not happen */
			elog(ERROR, "cache lookup failed for index %u", indexoid);
		result = ((Form_pg_index) GETSTRUCT(indexTuple))->indisprimary;
		ReleaseSysCache(indexTuple);
		if (result)
			break;
	}

	list_free(indexoidlist);

	return result;
}

/*
 * relationHasUniqueIndex -