Efficiency issues with Oracle query logging

The recent optimization of Oracle database efficiency, and then on the Internet to check the existence of a number of high-efficiency methods
There are a lot of suggestions on the Internet first method, I did a test, but probably not enough data volume, 42,667 Records, do not know what a large amount of data is a situation

Many highly efficient ways to advise online

SELECT * from item where item= ' 1b241371x0021 ' and rownum<2;

But the result of my test:

SELECT * from item where item= ' 1b241371x0021 ' and rownum<2;

1 rows selected in 0.047 seconds

COUNT (*) mode

Select COUNT (*) from item where item= ' 1b241371x0021 ';

1 rows selected in 0.016 seconds

Exists way

Select COUNT (*) from the dual where exists (select 1 from item where item= ' 1b241371x0021 ');

1 rows selected in 0.015 seconds

From the test results, the latter two methods are significantly more efficient than the previous one.

Efficiency issues with Oracle query logging