Structured Query Language (SQL) - Cultural View of Technology

Data Definition Language 34
The DROP statement is distinct from the DELETE and (non-standard) TRUNCATE statements, in that they do not
remove the table itself. For example, a DELETE statement might delete some (or all) data from a table while leaving
the table itself in the database, whereas a DROP statement would remove the entire table from the database.
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). The types of objects that can be altered depends on which RDBMS is being used.
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 key and foreign key tags in some columns of the tables.
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).
DDL Tools and Related Applications
Apache DdlUtils
Apache DdlUtils [1] 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
References
[1] http://db.apache.org/ddlutils/