Oracle Parallel usage

Oracle Parallel uses oracle Parallel (Parallel) to use 1. query the SQL code SELECT/* + Parallel (t, 8) */* FROM emp t; SELECT/* + Parallel (8) */* FROM emp t; SELECT/* + Parallel */* FROM emp t; 2. SQL code for creating an index: create index idx_emp_test on emp (empno, ename, job) nologging parallel 32; when creating an index, you must add parallel operations if conditions are met! The ExaData server on the customer side creates an index for the waybill table (more than 50 million records, more than 90 fields, more than 60 GB Data). The index field contains 6 columns, and the degree of parallelism is up to 64, it took only 13 seconds to create an index ...... 3. execute the table analysis SQL code EXEC DBMS_STATS.GATHER_TABLE_STATS (ownname => 'Scott ', tabname => 'emp', degree => 32, cascade => true); 4. INSERT SQL code INSERT/* + append parallel (30) */INTO t_a SELECT/* + parallel (30) */FROM t_ B -- PS: an individual uses insert select on the ExaData server for testing. After insert and Append are added, there is no difference in addition to Parallel. I don't know why. however, the following select statements without Parallel differ greatly.