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.
Primary key not null in SQL Server. A Jr. Developer asked me why a primary key not null in SQL Server. A primary key uniquely identifies a row in a table and a NULL canât identify any row. Moreover, a primary key is used to find rows in a table and is essential for indexing and maintaining data. Letâs see what happens if we try to add a primary key constraint on a null able column. As shown in above image, the SQL Server terminates with error when creating primary key on a null able column. Letâs see the behavior when defining composite primary key. The SQL Server again terminates with error.