RDBMS,
  • A dual table is oracle’s in built table.
  • It can be used for arithmetic calculations.
  • We can retrieve data from the dual table but cannot insert the data.
  • It has only single row and signal column.
  • Structure of dual table is as follow.
  • DESC dual;
Name Type Null?
Dummy Varchar2 (1)
  • Column name is dummy with data type varchar2 and size=1.
  • It contains value ‘X’.

Example:

SELECT 20*7 FROM DUAL;
SELECT sum(10,20,30) FROM DUAL;
SELECT max(10,20,30) FROM DUAL;