Table (database)

Information about Table (database)

In relational databases, SQL databases, and flat file databases, a table is a set of data elements (values) that is organized using a model of horizontal rows and vertical columns. The columns are identified by name, and the rows are identified by the values appearing in a particular column subset which has been identified as a candidate key. Table is another term for relations; although there is the difference in that a table is usually a multi-set (bag) of rows whereas a relation is a set and does not allow duplicates. A table has a specified number of columns but can have any number of rows. Besides the actual data rows, tables generally have associated with them some meta-information, such as constraints on the table or on the values within particular columns.

The data in a table does not have to be physically stored in the database. Views are also relational tables, but their data is calculated at query time. Another example are nicknames, which represent a pointer to a table in another database.

Comparisons with other data structures

In non-relational systems, such as hierarchical databases, the distant counterpart of a table is a structured file, representing the rows of a table in each record of the file and each column in a record.

Unlike a spreadsheet, the datatype of each field is ordinarily defined by the schema describing the table. Some relational systems are less strict about field datatype definitions.

Tables versus relations

In terms of the relational model of databases, a table can be considered a convenient representation of a relation, but the two are not strictly equivalent. For instance, an SQL table can potentially contain duplicate rows, whereas a true relation cannot contain duplicate tuples. Similarly, representation as a table implies a particular ordering to the rows and columns, whereas a relation is explicitly unordered. However, the database system does not guarantee any ordering of the rows unless an ORDER BY clause is specified in the SELECT statement that queries the table.

An equally valid representation of a relation is as an n-dimensional graph, where n is the number of attributes (a table's columns). For example, a relation with two attributes and three values can be represented as a table with two columns and three rows, or as a two-dimensional graph with three points. The table and graph representations are only equivalent if the ordering of rows is not significant, and the table has no duplicate rows.

Flat files

A flat file is a file that contains records, and in which each record is specified in a single line.
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In the context of a relational database, a row—also called a record or tuple—represents a single, implicitly structured data item in a table. In simple terms, a database table can be thought of as consisting of rows and columns or fields.
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In the context of a relational database table, a column is a set of data values of a particular simple type, one for each row of the table.^[1] The columns provide the structure according to which the rows are composed.
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In the relational model, a candidate key of a relvar (relation variable) 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

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The relational model for database management is a database model based on predicate logic and set theory. It was first formulated and proposed in 1969 by Edgar Codd with aims that included avoiding, without loss of completeness, the need to write computer programs to
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Metadata is data about data. An item of metadata may describe an individual datum, or content item, or a collection of data including multiple content items.

Metadata (sometimes written 'meta data') is used to facilitate the understanding, use and management of data.
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A check constraint (also known as table check constraint) is a condition that defines valid data when adding or updating an entry in a table of a relational database. A check constraint is applied to each row in the table. The constraint must be a predicate.
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In database theory, a view is a virtual or logical table composed of the result set of a query. Unlike ordinary tables (base tables) in a relational database, a view is not part of the physical schema: it is a dynamic, virtual table computed or collated from data in the database.
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In a hierarchical data model, data are organized into a tree-like structure. The structure allows repeating information using parent/child relationships: each parent can have many children but each child only has one parent.
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computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage.
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spreadsheet is a rectangular table (or grid) of information, often financial information. The word came from "spread" in its sense of a newspaper or magazine item (text and/or graphics) that covers two facing pages, extending across the center fold and treating the two pages as one
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In programming languages a data type defines a set of values and the allowable operations on those values^[1]. For example, in the Java programming language, the "int" type represents the set of 32-bit integers ranging in value from -2,147,483,648 to 2,147,483,647, and
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A Logical Schema is a data model of a specific problem domain that is in terms of a particular data management technology. Without being specific to a particular database management product, it is in terms of either (for example, in 2007) relational tables and columns,
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relation or relationship is a generalization of 2-place relations, such as the relation of equality, denoted by the sign "=" in a statement like "5 + 7 = 12," or the relation of order,
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For the musical term, see .

In mathematics, a tuple is a finite sequence (also known as an "ordered list") of objects, each of a specified type. A tuple containing n objects is known as an "n-tuple".
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An ORDER BY clause in SQL specifies that a SQL SELECT statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria does not have to be included in the result set.
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An SQL SELECT statement returns a result set of records from one or more tables.

It retrieves zero or more rows from one or more base tables, temporary tables, or views in a database.
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Graph may refer to:

A chart, a graphic representing tabular data or functions
A graph used in visualising scientific data, representing the relationship between two or more variables

In mathematics:

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table is both a mode of visual communication and a means of arranging data. The use of tables is pervasive throughout all communication, research and data analysis. Tables appear in print media, handwritten notes, computer software, architectural ornamentation, traffic signs and
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A database management system (DBMS) is computer software designed for the purpose of managing databases. Typical examples of DBMSs include Oracle, DB2, Microsoft Access, Microsoft SQL Server, PostgreSQL, MySQL, FileMaker and Sybase Adaptive Server Enterprise.
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database is a structured collection of records or data that is stored in a computer system so that a computer program or person using a query language can consult it to answer queries. The records retrieved in answer to queries are information that can be used to make decisions.
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A data model is not just a way of structuring data: it also defines a set of operations that can be performed on the data. The relational model, for example, defines operations such as select, project, and join.
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flat file database describes any of various means to encode a data model (most commonly a table) as a plain text file.

Unordered

Unordered storage typically stores the records in the order they are inserted, while having
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A distributed database management system is a software system that permits the management of a distributed database and makes the distribution transparent to the users. A distributed database is a collection of multiple, logically interrelated databases distributed over a computer network.
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ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction.
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Topics in database management systems (DBMS) • • [ edit]
Concepts Database Database models Database storage Relational model Distributed DBMS ACID Null Relational database Relational algebra Relational calculus Database normalization Referential integrity Relational DBMS Primary key, Foreign key, Surrogate key, Superkey, Candidate key
Objects Trigger View Table Cursor Log Transaction Index Stored procedure Partition	Topics in SQL Select Insert Update Merge Delete Join Union Create Drop Begin work Commit Rollback Truncate Alter
Implementations of database management systems
Types of implementations Relational Flat file Deductive Dimensional Hierarchical Object oriented Object relational Temporal XML data stores
Database products Object-oriented (comparison) Relational (comparison)	Components Query language Query optimizer Query plan ODBC JDBC

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