DATABASE LANGUAGES

Data Defunition Language (DDL)

Data Definition Language is used to define the database conceptual schema. In most DBMS, the DDL also defines user views and sometimes storage structures. The DBMS will have a DDL compiler whose function is to process DDL statements in order to identify descriptions of the schema constructs and to store the schema description in the DBMS catalog. In other DBMSs, separate languages -View Definition Language (VDL), Storage Definition Language (SDL) - may exist for specifying views and storage structures.

DDL statements are used to alter/modify a database or table structure and schema. These statements handle the design and storage of database objects;

CREATE – create a new Table, database, schema

ALTER   – alter existing table, column description

DROP    – delete existing objects from database

Data Manipulation Language (DML)

A data manipulation language (DML) is a family of computer languages including commands permitting users to manipulate data in a database. This manipulation involves inserting data into database tables, retrieving existing data, deleting data from existing tables and modifying existing data. DML is mostly incorporated in SQL databases.

DML statements affect records in a table. These are basic operations we perform on data such as selecting a few records from a table, inserting new records, deleting unnecessary records, and updating/modifying existing records.

DML statements include the following:

SELECT – select records from a table

INSERT – insert new records

UPDATE – update/Modify existing records

DELETE – delete existing records