Whether the Oracle query records are efficient or not.

Whether the Oracle query records are efficient or not.

Recently, we need to optimize the efficiency of the Oracle database, and then check a lot of efficient methods on the Internet to determine whether the record exists.
There are many suggestions for the first method on the Internet. I did a test, but the data volume may not be large enough, with 42667 records. I don't know what a large data volume is.

Many efficient recommendations on the Internet

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

But my test results:

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

1 rows selected in 0.047 seconds

Count (*) Method

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

1 rows selected in 0.016 seconds

Exists Method

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

1 rows selected in 0.015 seconds

From the test results, the efficiency of the last two methods is significantly higher than that of the previous method.