A Data Definition Language (DDL) is a computer language for defining data structures. The term was first introduced in relation to the Codasyl database model, where the schema of the database was written in a Data Definition Language describing the records, fields, and "sets" making up the user Data Model. Initially it referred to a subset of SQL, but is now used in a generic sense to refer to any formal language for describing data or information structures, like XML schemas. Look up computer language & a Brief History of it in Wiktionary, the free dictionary. ... A binary tree, a simple type of branching linked data structure. ... CODASYL (often spelt Codasyl) is an acronym for COnference on DAta SYstems Languages. This was a IT industry consortium formed in 1959 to guide the development of a standard programming language that could be used on many computers. ... The word schema comes from the Greek word σχήμα (skhēma) that means shape or more generally plan. ... A data model is a model that describes how data are represented and used in an abstract way. ...

SQL

A subset of SQL's instructions form another DDL. These SQL statements define the structure of a database, including rows, columns, tables, indexes, and database specifics such as file locations. DDL SQL statements are more part of the DBMS and have large differences between the SQL variations. DDL SQL commands include the following: SQL (IPA: or ) is a computer language designed for the retrieval and management of data in relational database management systems, database schema creation and modification, and database object access control management. ... This article is about computing. ... A database management system (DBMS) is a computer program (or more typically, a suite of them) designed to manage a database, a large set of structured data, and run operations on the data requested by numerous users. ...

CREATE statements

Create - To make a new database, table, index, or stored query. A CREATE statement in SQL creates an object inside of a relational database management system (RDBMS). The types of objects that can be created depends on which RDBMS is being used, but most support the creation of tables, indexes, users, and databases. Some systems (such as PostgreSQL) allow CREATE, and other DDL commands, inside of a transaction and thus they may be rolled back. SQL (IPA: or ) is a computer language designed for the retrieval and management of data in relational database management systems, database schema creation and modification, and database object access control management. ... A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. ... 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. ... A database index is a data structure that improves the speed of operations in a table. ... This article is about computing. ... PostgreSQL is a free software object-relational database management system (ORDBMS), released under a BSD-style license. ... 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. ... In database technologies, a rollback is an operation which returns the database to some previous state. ...

CREATE TABLE

Perhaps the most common CREATE command is the CREATE TABLE command. The typical usage is:

CREATE [TEMP[ORARY]] TABLE [table name] ( [column definitions] ) [table parameters].

Column Definitions: A comma-separated list consisting of any of the following

• Column definition: [column name] [data type] {NULL | NOT NULL} {column options}
• Primary key definition: PRIMARY KEY ( [comma separated column list] )
• CONSTRAINTS: {CONSTRAINT} [constraint definition]
• RDBMS specific functionality

For example, the command to create a table named employees with a few sample columns would be: In database design, a primary key is a value that can be used to identify a unique row in a table. ... A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. ...

 CREATE TABLE employees ( id INTEGER PRIMARY KEY, first_name CHAR(50) NULL, last_name CHAR(75) NOT NULL, date_of_birth DATE NULL ); 

DROP statements

Drop - To destroy an existing database, table, index, or view. A DROP statement in SQL removes an object from a relational database management system (RDBMS). ...

A DROP statement in SQL removes an object from a relational database management system (RDBMS). The types of objects that can be dropped depends on which RDBMS is being used, but most support the dropping of tables, users, and databases. Some systems (such as PostgreSQL) allow DROP and other DDL commands to occur inside of a transaction and thus be rolled back. SQL (IPA: or ) is a computer language designed for the retrieval and management of data in relational database management systems, database schema creation and modification, and database object access control management. ... A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. ... 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. ... This article is about computing. ... PostgreSQL is a free software object-relational database management system (ORDBMS), released under a BSD-style license. ... 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. ... In database technologies, a rollback is an operation which returns the database to some previous state. ...

The typical usage is simply DROP objecttype objectname. For example, the command to drop a table named employees would be:

 DROP TABLE employees; 

The DROP statement is distinct from the DELETE statement. For example, a DELETE statement might delete some (or all) data from a table, whereas a DROP statement might remove the entire table from the database. An SQL DELETE statement removes one or more records from a table. ...

ALTER statements

Alter - To modify an existing database object. An ALTER statement in SQL changes the properties of an object inside of a relational database management system (RDBMS). ...

An ALTER statement in SQL changes the properties of an object inside of a relational database management system (RDBMS). The types of objects that can be altered depends on which RDBMS is being used. SQL (IPA: or ) is a computer language designed for the retrieval and management of data in relational database management systems, database schema creation and modification, and database object access control management. ... A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd. ...

The typical usage is ALTER objecttype objectname parameters. For example, the command to add (then remove) a column named bubbles for an existing table named sink would be:

 ALTER TABLE sink ADD bubbles INTEGER; ALTER TABLE sink DROP COLUMN bubbles; 

Referential integrity statements

Finally, other kind of DDL sentence in SQL are the statements to define referential integrity relationships, usually implemented as primary keys and foreign keys tags in some columns of the tables. An example of a database that has not enforced referential integrity. ... In database design, a primary key is a value that can be used to identify a unique row in a table. ... In the context of relational databases, a foreign key is a referential constraint between two tables[1]. The foreign key identifies a column or a set of columns in one (referencing) table that refers to a column or set of columns in another (referenced) table. ...

These two statements can be included inside a CREATE TABLE or an ALTER TABLE sentence.

XML Schema

XML Schema is an example of a pure DDL (although only relevant in the context of XML). This article is about the W3Cs XML Schema language. ... The Extensible Markup Language (XML) is a general-purpose markup language. ...

DDL Tools and Related Applications

Apache DdlUtils

Apache DdlUtils is a small, easy-to-use component for working with Database Definition (DDL) files. These are XML files that contain the definition of a database schema, e.g. tables and columns. These files can be fed into DdlUtils via its Ant task or programmatically in order to create the corresponding database or alter it so that it corresponds to the DDL. Likewise, DdlUtils can generate a DDL file for an existing database.

See also

• Data Manipulation Language
• Data Control Language