Oracle Database DUAL table
Remarks
DUAL table has one column DUMMY, defined to be VARCHAR2(1) and only one row with a value x.
DUAL table is automatically created in SYS schema when database is created. You can access it from any schema.
You can not change DUAL table.
You can use DUAL table to call any function from SQL statement. It is useful because it has only one row and oracle optimizer knows everything about it.
