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Oracle SQL Plan operation FAST DUAL

The row source FAST DUAL is used when selecting an expression which does not involve DUMMY from dual.

The plan for select * from dual (which implicitely selects DUMMY by means of the *) selects from DUAL with full table access:

explain plan for
   select * from dual;
   
select * from table(dbms_xplan.display(format=>'basic'));
--
-- ----------------------------------
-- | Id  | Operation         | Name |
-- ----------------------------------
-- |   0 | SELECT STATEMENT  |      |
-- |   1 |  TABLE ACCESS FULL| DUAL |
-- ----------------------------------

However, when selecting an «ordinary» expression from dual, the FAST DUAL row source is used:

explain plan for
   select sysdate from dual;
   
select * from table(dbms_xplan.display(format=>'basic'));
--
-- ---------------------------------
-- | Id  | Operation        | Name |
-- ---------------------------------
-- |   0 | SELECT STATEMENT |      |
-- |   1 |  FAST DUAL       |      |
-- ---------------------------------

Oracle SQL Plan operation FAST DUAL

See also