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.