只搜索到官方的这个hint，没有表的default说明
For a statement-level PARALLEL hint:
■ PARALLEL: The statement always is run parallel, and the database computes the degree of parallelism, which can be 2 or greater.
■ PARALLEL (DEFAULT): The same as PARALLEL. The DEFAULT keyword is included for completeness.
■ PARALLEL (AUTO): The database computes the degree of parallelism, which can be 1 or greater. If the computed degree of parallelism is 1, then the statement runs serially.
■ PARALLEL (MANUAL): The optimizer is forced to use the parallel settings of the objects in the statement.
■ PARALLEL (integer): The optimizer uses the degree of parallelism specified by integer.

跟parallel_degree_policy参数有关，在默认情况下，该参数值为manual，此时如果配置表的degree为default，正常查询（不带hint），也会有并行查询的情况，并行度为cpu