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A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for maintaining the integrity of the information on the database. For example, when a new record (representing a new worker) is added to the employees table, new records ...
e. A database right is a sui generis property right, comparable to but distinct from copyright, that exists to recognise the investment that is made in compiling a database, even when this does not involve the "creative" aspect that is reflected by copyright. [1] Such rights are often referred to in the plural: database rights .
In SQL, null or NULL is a special marker used 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 ...
Relational database. A relational database ( RDB [1]) is a database based on the relational model of data, as proposed by E. F. Codd in 1970. [2] A database management system used to maintain relational databases is a relational database management system ( RDBMS ). Many relational database systems are equipped with the option of using SQL ...
Entity–relationship model. An entity–attribute-relationship diagram for an MMORPG using Chen's notation. An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships ...
View (SQL) In a database, a view is the result set of a stored query, which can be queried in the same manner as a persistent database collection object. [1] This pre-established query command is kept in the data dictionary. Unlike ordinary base tables in a relational database, a view does not form part of the physical schema: as a result set ...
eXist-db (or eXist for short) is an open source software project for NoSQL databases built on XML technology. It is classified as both a NoSQL document-oriented database system and a native XML database (and it provides support for XML, JSON, HTML and Binary documents). Unlike most relational database management systems (RDBMS) and NoSQL ...
The EXISTS condition uses the SQL standard keyword EXISTS to determine whether rows exist in a subquery result. Examples. To SELECT one row of data from a table called tab with a primary key column (pk) set to 100 — use the condition pk = 100: