Structured Query Language (SQL) Overview

Non-procedural (declarative) language common to most relational database systems.

– Used by the database system to "manage" itself internally and by users to manipulate and query the data.

– Uses set theory (as opposed to row processing) to process requests.

– Has a limited but flexible set of commands.

– Free-form for the most part, uses semi-colon as statement terminator in most databases.

Knowledge of SQL should enable

– moving easily from one database system to another

– writing queries that cannot be represented in the graphical user interface

– troubleshooting

– analyzing queries for performance (tuning)

SQL commands classified by function:

– Data definition language (DDL) - used to define or change database structure(s)

CREATE

ALTER

DROP

– Data manipulation language (DML) - used to select or change data

INSERT

UPDATE

DELETE

SELECT

– Data control language (DCL) - used to control user access (e.g., GRANT, REVOKE)

– Transactional language - used to control logical units of work (e.g., COMMIT)