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PostgreSQL, MySQL and Oracle support natural joins; Microsoft T-SQL and IBM DB2 do not. The columns used in the join are implicit so the join code does not show which columns are expected, and a change in column names may change the results. In the SQL:2011 standard, natural joins are part of the optional F401, "Extended joined table", package.
In database design, a composite key is a candidate key that consists of two or more attributes, [1] [2] [3] (table columns) that together uniquely identify an entity occurrence (table row). A compound key is a composite key for which each attribute that makes up the key is a foreign key in its own right.
A candidate key, or simply a key, of a relational database is any set of columns that have a unique combination of values in each row, with the additional constraint that removing any column could produce duplicate combinations of values. A candidate key is a minimal superkey, [1] i.e., a superkey that does not contain a smaller one. Therefore ...
A foreign key is a set of attributes in a table that refers to the primary key of another table, linking these two tables. In the context of relational databases, a foreign key is subject to an inclusion dependency constraint that the tuples consisting of the foreign key attributes in one relation, R, must also exist in some other (not necessarily distinct) relation, S; furthermore that those ...
Formally, a "database" refers to a set of related data accessed through the use of a "database management system" (DBMS), which is an integrated set of computer software that allows users to interact with one or more databases and provides access to all of the data contained in the database (although restrictions may exist that limit access to particular data).
The operation of Wikipedia depends on MediaWiki, a custom-made, free and open source wiki software platform written in PHP and built upon the MySQL database system. [W 71] The software incorporates programming features such as a macro language, variables, a transclusion system for templates, and URL redirection.
In April 2007, a rumour was confirmed on the Swedish talk show Bert that The Pirate Bay had received financial support from right-wing entrepreneur Carl Lundström. This caused some consternation since Lundström, an heir to the Wasabröd fortune, is known for financing several far-right political parties and movements like Sverigedemokraterna and Bevara Sverige Svenskt (Keep Sweden Swedish).
Twitter, officially known as X since 2023, is a social networking service.It is one of the world's largest social media platforms and one of the most-visited websites. [4] [5] Users can share short text messages, images, and videos in short posts commonly known as "tweets" (officially "posts") and like other users' content. [6]