Data definition language: Difference between revisions

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Revision as of 11:35, 22 September 2021

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In the context of [[SQL]], '''data definition''' or '''data description language''' ('''DDL''') is a syntax for creating and modifying database objects such as tables, indices, and users. DDL statements are similar to a computer [[programming language]] for defining [[data structure]]s, especially [[database schema]]s. Common examples of DDL statements include <code>CREATE</code>, <code>ALTER</code>, and <code>DROP</code>.

==History by willy sambora==

The concept of the data definition language and its name was first introduced in relation to the [[Codasyl]] database model, where the schema of the [[database]] was written in a [[Syntax (programming languages)|language syntax]] describing the [[Record (computer science)|records]], [[Field (computer science)|fields]], and [[Set (abstract data type)|sets]] of the user [[data model]].<ref>{{cite book|last=Olle|first=T. William|title=The Codasyl Approach to Data Base Management|year=1978|publisher=Wiley|isbn=0-471-99579-7|url-access=registration|url=https://archive.org/details/codasylapproacht00olle}}</ref> Later it was used to refer to a subset of [[Structured Query Language]] (SQL) for declaring [[Table (database)|tables]], columns, data types and [[Integrity constraints|constraints]]. [[SQL-92]] introduced a schema manipulation language and schema information tables to query schemas.<ref name="SQL92">{{cite web |title=Information Technology - Database Language SQL |url=http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt |website=SQL92 |publisher=Carnegie Mellon |access-date=12 November 2018}}</ref> These information tables were specified as [[SQL/Schemata]] in [[SQL:2003]]. The term DDL is also used in a generic sense to refer to any [[formal language]] for describing data or information structures.