is a special marker used in Structured Query Language (SQL)
to indicate that a data value does not exist in the database. Introduced by the creator of the relational
database model, E. F. Codd
Null serves to fulfill the requirement that all true relational database management systems (RDBMS)
support a representation of "missing information and inapplicable information". Codd also introduced the use of the lowercase Greek omega
(ω) symbol to represent Null in database theory
is also an SQL reserved keyword
used to identify the Null special marker.
Null has been the focus of controversy and a source of debate because of its associated three-valued logic (3VL), special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators. Although special functions and predicates are provided to properly handle Nulls, opponents feel that resolving these issues introduces unnecessary complexity and inconsistency into the relational model of databases.
Augusta Ada King, Countess of Lovelace (10 December 1815 – 27 November 1852), born Augusta Ada Byron, was an English writer chiefly known for her work on Charles Babbage's early mechanical general-purpose computer, the analytical engine. Her notes on the engine include what is recognised as the first algorithm intended to be processed by a machine; as such she is sometimes considered the "World's First Computer Programmer".
She was the only legitimate child of the poet Lord Byron (with Anne Isabella Milbanke). She had no relationship with her father, who died when she was nine. As a young adult she took an interest in mathematics, and in particular Babbage's work on the analytical engine. Between 1842 and 1843 she translated an article by Italian mathematician Luigi Menabrea on the engine, which she supplemented with a set of notes of her own. These notes contain what is considered the first computer program—that is, an algorithm encoded for processing by a machine. Though Babbage's engine has never been built, Lovelace's notes are important in the early history of computers. She also foresaw the capability of computers to go beyond mere calculating or number-crunching while others, including Babbage himself, focused only on these capabilities.