The dual Table

The dual Table



1. dual is a table that contains a single row.
2. The dual table has one VARCHAR2 column named dummy.
3. 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

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Understanding Null Values


1. A database use null value to represent a unknown value.
2. A null value is not a blank string.
3. A null value means the value for the column is unknown.
4. When you select a column that contains a null value, you see nothing in that column.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++