I'm working with Oracle databases (version 19 for now), and I always wondered about the weird DUAL table1 that I require in my work.
Things like this:
select sysdate from dual;
select seq_s_ordertable.nextval from dual;
select seq_s_ordertable.nextval from dual;
Well, apparently we have Charles "Chuck" Weiss2 to thank for it.
One of the reasons is that the FROM clause in Oracle SQL syntax is mandatory.
Interestingly, Charles originally created the DUAL table with two rows, hence the name DUAL. Nowadays it's one row, but the name's stuck.
It's part of the Data Dictionary of the SYS user. Changing the DUAL table will cause problems!3
References
- [1] Wikipedia - DUAL table
- https://en.wikipedia.org/wiki/DUAL_table
- [2] Wikipedia - Charles Weiss
- https://en.wikipedia.org/wiki/Charles_Weiss
- [3] Ask tom - All about the DUAL table
- https://asktom.oracle.com/ords/f?p=100:11:0::::P11_QUESTION_ID:1562813956388
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