Null may refer to:
NULL
, nil
, or None
), used in computer programming for an uninitialized, undefined, empty, or meaningless valueIn mathematics, the word null (from German: null meaning "zero", which is from Latin: nullus meaning "none") means of or related to having zero members in a set or a value of zero. Sometimes the symbol ∅ is used to distinguish "null" from 0. is sometimes called Aleph null.
In a normed vector space the null vector is the zero vector; in a seminormed vector space such as Minkowski space, null vectors are, in general, non-zero. In set theory, the null set is the set with zero elements; and in measure theory, a null set is a set with zero measure.
A null space of a mapping is the part of the domain that is mapped into the null element of the image (the inverse image of the null element).
In statistics, a null hypothesis is a proposition presumed true unless statistical evidence indicates otherwise.
Null is a Foetus EP released in 1995 by Big Cat in the UK. Null acts as a De facto single for "Verklemmt," released on Gash. Promotional copies of Null were distributed by Sony/Columbia in the US, but the EP had no official US release. Null was later rereleased as half of the Null/Void double-CDEP set.
All songs written and composed by J. G. Thirlwell.
Null is the first EP by the American post-metal band Intronaut. It was released in 2006 on Goodfellow Records.
In radio electronics, a null is an area or vector in an antenna's radiation pattern where the signal cancels out almost entirely.
This can be an advantage, as nulls in the horizontal plane can be used to protect other transmitters from interference. If not carefully planned however, nulls can unintentionally prevent reception of a signal. Null fill in the vertical plane is used to prevent this.
Also, some directional antennas have very narrow, sharp nulls. These antennas when used for direction finding are aimed away from the signal of interest until the antenna's null is pointed at the signal, and the signal cannot be detected.
Null 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, SQL 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. NULL
is also an SQL reserved keyword used to identify the Null special marker.
For people new to the subject, a good way to remember what null means is to remember that in terms of information, "lack of a value" is not the same thing as "a value of zero"; similarly, "lack of an answer" is not the same thing as "an answer of no". For example, consider the question "How many books does Juan own?" The answer may be "zero" (we know that he owns none) or "null" (we do not know how many he owns, or doesn't own). In a database table, the column reporting this answer would start out with no value (marked by Null), and it would not be updated with the value "zero" until we have ascertained that Juan owns no books.