Function op_mergejoinable

src/backend/utils/cache/lsyscache.c:1529–1567

* op_mergejoinable * * Returns true if the operator is potentially mergejoinable. (The planner * will fail to find any mergejoin plans unless there are suitable btree * opfamily entries for this operator and associated sortops. The pg_operator * flag is just a hint to tell the planner whether to bother looking.) * * In some cases (currently only array_eq and record_eq), mergejoinability

 * is needed to check this --- by convention, pass the left input's data type.
 */
bool
op_mergejoinable(Oid opno, Oid inputtype)
{
	bool		result = false;
	HeapTuple	tp;
	TypeCacheEntry *typentry;

	/*
	 * For array_eq or record_eq, we can sort if the element or field types
	 * are all sortable.  We could implement all the checks for that here, but
	 * the typcache already does that and caches the results too, so let's
	 * rely on the typcache.
	 */
	if (opno == ARRAY_EQ_OP)
	{
		typentry = lookup_type_cache(inputtype, TYPECACHE_CMP_PROC);
		if (typentry->cmp_proc == F_BTARRAYCMP)
			result = true;
	}
	else if (opno == RECORD_EQ_OP)
	{
		typentry = lookup_type_cache(inputtype, TYPECACHE_CMP_PROC);
		if (typentry->cmp_proc == F_BTRECORDCMP)
			result = true;
	}
	else
	{
		/* For all other operators, rely on pg_operator.oprcanmerge */
		tp = SearchSysCache1(OPEROID, ObjectIdGetDatum(opno));
		if (HeapTupleIsValid(tp))
		{
			Form_pg_operator optup = (Form_pg_operator) GETSTRUCT(tp);

			result = optup->oprcanmerge;
			ReleaseSysCache(tp);
		}
	}
	return result;
}

/*
 * op_hashjoinable