Dual is a virtual table used to form the syntax rules of select. Oracle guarantees that there is always only one record in the dual. We can do many things with it, as follows:
1. To view the current user, you can execute the following statement in SQL Plus to select user from dual;
2. Used to call system functions
select to_char(sysdate,'yyyy-mm-dd hh24:mi:ss') from dual;--get the current system time
select SYS_CONTEXT('USERENV','TERMINAL') from dual;--get hostname
select SYS_CONTEXT('USERENV','language') from dual;--get the current locale
select dbms_random.random from dual;--get a random number
3. To get the next value or current value of the sequence, use the following statement
select your_sequence.nextval from dual;--get the next value of the sequence your_sequence
select your_sequence.currval from dual;--get the current value of the sequence your_sequence
4. Can be used as a calculator select 7*9 from dual;