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A superkey is defined in the relational model as a set of attributes of a relation variable (relvar) for which it holds that in all relations assigned to that variable there are no two distinct tuples (rows) that have the same values for the attributes in this set. Equivalently a superkey can also be defined as a set of attributes of a relvar upon which all attributes of the relvar are functionally dependent. The relational model for database management is a database model based on predicate logic and set theory. ...
In mathematics, a set can be thought of as any collection of distinct things considered as a whole. ...
In mathematics, a tuple is a finite sequence of objects, that is, a list of a limited number of objects. ...
A functional dependency is a constraint between two sets of attributes in a relation from a database. ...
Note that if attribute set K is a superkey of relvar R, then at all times it is the case that the projection of R over K has the same cardinality as R itself.
Informally, a superkey is a set of columns within a table whose values can be used to uniquely identify a row. A candidate key is a minimal set of columns necessary to identify a row, this is also called a minimal superkey. For example, given an employee table, consisting of the columns employeeID, name, job, and departmentID, we could use the employeeID in combination with any or all other columns of this table to uniquely identify a row in the table. Examples of superkeys in this table would be {employeeID, Name}, {employeeID, Name, job}, and {employeeID, Name, job, departmentID}. In the relational model a candidate key of a relation variable (relvar) is a set of attributes of that relvar such that (1) at all times it holds in the relation assigned to that variable that there are no two distinct tuples with the same values for these attributes and...
In a real database we don't need values for all of those columns to identify a row. We only need, per our example, the set {employeeID}. This is a minimal superkey—that is, a minimal set of columns that can be used to identify a single row. So, employeeID is a candidate key. In the relational model a candidate key of a relation variable (relvar) is a set of attributes of that relvar such that (1) at all times it holds in the relation assigned to that variable that there are no two distinct tuples with the same values for these attributes and...
Example Vehicle ID # | State | Plate # | Color ------------------------------------- 10000000001 | CM | 333 | Red 10000000002 | GA | 399 | Blue 10000000003 | FL | 333 | BLUE In this example a superkey can be either {Vehicle ID}, {Vehicle ID, State}, {Vehice ID, State, Plate#}, {State} or {State, Plate#}
See also
| Topics in database management systems (DBMS) ( view • talk • edit ) | | Concepts
Database | Database model | Relational database | Relational model | Relational algebra | Primary key - Foreign key - Surrogate key - Superkey
Database normalization | Referential integrity | Relational DBMS | Distributed DBMS | ACID In database design, a compound key (also called a composite key) is a key that consists of 2 or more attributes. ...
In the relational model a candidate key of a relation variable (relvar) is a set of attributes of that relvar such that (1) at all times it holds in the relation assigned to that variable that there are no two distinct tuples with the same values for these attributes and...
In database design, a primary key is a value that can be used to identify a unique row in a table. ...
An alternate key is any candidate key which is not selected to be the primary key. ...
A foreign key (FK) is a field or group of fields in a database record that point to a key field or group of fields forming a key of another database record in some (usually different) table. ...
To meet Wikipedias quality standards, this article or section may require cleanup. ...
The term database originated within the computer industry, though its meaning has been broadened by popular use,includes non-electronic databases within its definition. ...
A database model is a theory or specification describing how a database is structured and used. ...
A relational database is a database that conforms to the relational model, and refers to a databases data and schema (the databases structure of how that data is arranged). ...
The relational model for database management is a database model based on predicate logic and set theory. ...
Relational algebra, an offshoot of first-order logic, is a set of relations closed under operators. ...
In database design, a primary key is a value that can be used to identify a unique row in a table. ...
A foreign key (FK) is a field or group of fields in a database record that point to a key field or group of fields forming a key of another database record in some (usually different) table. ...
A surrogate key is a unique primary key generated by the relational database management system that is not derived from any data in the database and whose only significance is to act as the primary key. ...
This article or section is in need of attention from an expert on the subject. ...
An example of a database that has not enforced referential integrity. ...
A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by Edgar F. Codd. ...
According to Elmasri and Navathe (2004, p. ...
For other uses, see Acid (disambiguation). ...
| Objects
Trigger | View | Table | Cursor | Log | Transaction | Index | Stored procedure | Partition A database trigger is procedural code that is automatically executed in response to certain events on a particular table in a database. ...
Originally, in database theory, a view is a read only virtual or logical table composed of the result set of a query. ...
In relational databases and SQL databases a table is a set of data elements (values) that is organized using a model of horizontal rows and vertical columns. ...
In database packages, the term cursor refers to a control structure for the successive traversal (and potential processing) of records in a result set as returned by a query. ...
In in the field of databases in computer science, a transaction log (also database log or binary log) is a history of actions executed by a database management system to guarantee ACID properties over crashes or hardware failures. ...
A database transaction is a unit of interaction with a database management system or similar system that is treated in a coherent and reliable way independent of other transactions that must be either entirely completed or aborted. ...
An index is a feature in a database that allows quick access to the rows in a table. ...
A stored procedure is a subroutine available to applications accessing a relational database system. ...
A partition is a division of a logical database or its constituting elements into distinct independent parts. ...
| Topics in SQL
Select | Insert | Update | Merge | Delete | Join | Union | Create | Drop
Comparison of syntax SQL (commonly expanded to Structured Query Language — see History for the terms derivation) is the most popular computer language used to create, modify, retrieve and manipulate data from relational database management systems. ...
A SELECT statement in SQL returns a result set of records from one or more tables. ...
An SQL INSERT statement adds one or more records to a table in a relational database. ...
An UPDATE statement in SQL changes data in one or more records in a relational database management system. ...
Wikipedia does not have an article with this exact name. ...
A DELETE statement in SQL removes records in a relational database management system. ...
A join combines records from two or more tables in a relational database. ...
UNION Combines the results of two or more queries into a single result set consisting of all the rows belonging to all queries in the union. ...
A CREATE statement in SQL creates an object inside of a relational database management system (RDBMS). ...
A DROP statement in SQL removes an object from a relational database management system (RDBMS). ...
This article gives a brief summary of various SQL syntax differences used in popular SQL engines: DB2 Firebird / InterBase MySQL MSSQL Oracle PostgreSQL SQLite OpenLink Virtuoso // Notes: ↑ Types: TINYTEXT, TEXT, MEDIUMTEXT LONGTEXT A method to somehow escape identifiers (table, column names, etc), so they do not have to obey regular...
| | | Implementations of database management systems | | Types of implementations
Flat file | Deductive | Dimensional | Hierarchical | Object oriented | Temporal
Products
db4o | dBASE | Oracle | Caché | OpenLink Virtuoso | Sybase | Ingres | MySQL | SQLite | Microsoft SQL Server | PostgreSQL | InterBase | Firebird | DB2 | Informix | Helix database | Teradata | Comparison - relational | Comparison - object-relational A flat file database is described by a very simple database model, where all the information is stored in text files. ...
A deductive database system is a database system which can make deductions (ie: infer additional rules or facts) based on rules and facts stored in the (deductive) database. ...
A dimensional database is one which, rather than storing data in multiple two dimensional tables (as a relational databases does), represents key data entities as different dimensions. ...
To meet Wikipedias quality standards, this article or section may require cleanup. ...
In an object oriented database, information is represented in the form of objects like in object oriented programming. ...
A temporal database is a database management system with built-in time aspects, e. ...
There are very few or no other articles that link to this one. ...
dBASE III The correct title of this article is dBASE. The initial letter is capitalized because of technical restrictions. ...
An Oracle database consists of a collection of data managed by an Oracle database management system. ...
Caché is a proprietary M technology-based database management system from InterSystems. ...
The current version of the article or section reads like an advertisement. ...
Sybase SQL Server was the name of Sybase Corporations primary relational database management system product from 1987 to 1995. ...
Ingres (pronounced ingress) is a commercially supported, open-source relational database management system. ...
MySQL is a multithreaded, multi-user, SQL Database Management System (DBMS) with more than six million installations. ...
SQLite is an ACID-compliant relational database management system contained in a relatively small C library. ...
Microsoft SQL Server is a relational database management system (RDBMS) produced by Microsoft. ...
PostgreSQL is a free object-relational database server (database management system), released under a flexible BSD-style license. ...
InterBase is a relational database management system (RDBMS) currently developed and marketed by Borland Software Corporation. ...
Firebird (sometimes called FirebirdSQL) is a relational database management system offering many ANSI SQL-99 and SQL-2003 features. ...
DB2 is IBMs line of RDBMS (or, as IBM now calls it, data server) software products within IBMs broader Information Management software line. ...
Informix is a family of relational database management system products from IBM, acquired in 2001 from a company (also called Informix or Informix Software) which dates its origins back to 1980. ...
Helix is a pioneering database management system for the Apple Macintosh platform. ...
Teradata Teradata is a relational database management system initially created by the firm with the same name, founded in 1979. ...
It has been suggested that List of relational database management systems be merged into this article or section. ...
The following tables compare general and technical information for a number of object-relational database management systems. ...
| Components
Query language | Query optimizer | Query plan | ODBC | JDBC
Lists
List of object-oriented database management systems
List of relational database management systems
List of truly relational database management systems Query languages are computer languages used to make queries into databases and information systems. ...
The query optimizer is a component of database management system that is used to analyzes queries submitted to database server for execution, and then determines the optimal way to execute the query. ...
A query plan (or query execution plan) is an set of steps used to access information in a SQL relational database management system. ...
In computing, Open Database Connectivity (ODBC) provides a standard software API method for using database management systems (DBMS). ...
Java Database Connectivity, or JDBC, is an API for the Java programming language that defines how a client may access a database. ...
The following is a list of object-oriented database management systems. ...
It has been suggested that List of truly relational database management systems be merged into this article or section. ...
It has been suggested that this article or section be merged into List of relational database management systems. ...
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