Database Languages

DDL

For describing data and data structures a suitable description tool, a data definition language (DDL), is needed. With this help a data scheme can be defined and also changed later. Typical DDL operations (with their respective keywords in the structured query language SQL): Creation of tables and definition of attributes (CREATE TABLE ...) Change of tables by adding or deleting attributes (ALTER TABLE …) Deletion of whole table including content (!) (DROP TABLE …)

DML

Additionally a language for the descriptions of the operations with data like store, search, read, change, etc. the so-called data manipulation, is needed. Such operations can be done with a data manipulation language (DML). Within such languages keywords like insert, modify, update, delete, select, etc. are common. Typical DML operations (with their respective keywords in the structured query language SQL): Add data (INSERT) Change data (UPDATE) Delete data (DELETE) Query data (SELECT)

Often these two languages for the definition and manipulation of databases are combined in one comprehensive language. A good example is the structured query language SQL which is discussed in detail in lesson Structured Query Language SQL.