In addition to the the Commonwealth Ensign, there are three other official Australian ensigns: 1  The Australian Red Ensign - Merchant Navy, as for the Australian flag, but with a red field with white stars. 2  The Australian White Ensign - Royal Australian Navy - as for the Australian flag but with a white field and dark blue stars.
Null (or NULL) is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfil the requirement that all true relational database management systems (RDBMS) support a representation of missing information and inapplicable information.
The NVL function allows you to replace null values with a default value. If the value in the first parameter is null, the function returns the value in the second parameter. If the first parameter is any value other than null, it is returned unchanged. We know that COL1 in the test table contains null in all rows except the first.