Any difference between this two sql

Question

are there any difference between this two sql
-- table definition : create table test(col varchar2(20) not null)
select * from test where col like '%%'
--and
select * from test
any difference there? please give some detailed analysis. thx.

Answer 1

Also take care when there are indexes.
SQL> create unique index testtab_col on testtab( col );
Index created.
SQL> set autotrace on explain                                            
SQL> select * from testtab;
COL
col1                         
col2
Execution Plan
Plan hash value: 2692415588
| Id  | Operation         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |         |     3 |    21 |     3   (0)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| TESTTAB |     3 |    21 |     3   (0)| 00:00:01 |
Note
   - dynamic sampling used for this statement
SQL> select * from testtab where col like '%%';
COL
col1
col2
Execution Plan
Plan hash value: 2166828774
| Id  | Operation        | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT |             |     2 |    14 |     1   (0)| 00:00:01 |
|*  1 |  INDEX FULL SCAN | TESTTAB_COL |     2 |    14 |     1   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter("COL" LIKE '%%')
Note
   - dynamic sampling used for this statement
SQL>So no - bottom line is that these SQLs are different. They may look superficially the same and even under certain circumstances act the same. But they are not the same.