Description
----------- 
You are allowed to specify DUAL as a dummy table name in
situations where no tables are referenced, such as the
following SELECT statement:
 
SELECT 1 + 1 FROM DUAL;
 
+-------+
| 1 + 1 |
+-------+
| 2 |
+-------+
 
 DUAL is purely for the convenience of people who require
 that all SELECT statements should have
 FROM and possibly other clauses. MariaDB ignores the
 clauses. MariaDB does not require FROM DUAL if no tables
 are referenced.
 
FROM DUAL could be used when you only SELECT computed
values, but require a WHERE clause, perhaps to test that a
script correctly handles empty resultsets:
 
SELECT 1 FROM DUAL WHERE FALSE;
 
Empty set (0.00 sec)
 


URL: https://mariadb.com/kb/en/dual/