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dual is a table that contains a single row. The dual table has one VARCHAR2 column named dummy. dual contains a single row with the value X.

The structure of the dual table:

SQL> SQL> DESCRIBE dual;  Name         Null?    Type  DUMMY                 VARCHAR2(1)

SQL> SELECT * FROM dual; D - X SQL> SQL> SQL> select 123 * 456 from dual;    123*456 ----------      56088 SQL> SQL> select sysdate from dual; SYSDATE ---------- 26-10-2009 SQL>