1. How you will avoid your query from using indexes?
By changing the order of the columns that are used in the index, in the Where condition, or by concatenating the columns with some constant values.
2. If you are a DBA and you want to connect to some account for which you don't know the password?
1. Get the encrypted password from the PASSWORD column of DBA_USERS.
2. Change the password to a new password temporarily.
3. Reset the original password from the encrypted password.
3. Tables with no rows?
select owner,table_name
from dba_tables
where num_rows = 0
4. Top N(5) Query - using hiredate
Select * from (select empno,ename,hiredate from emp order by hiredate desc) where rownum<6;
