Structured Query
Language (SQL)
Non-procedural (declarative) language common to most relational database
systems.
–
Used
by the database system internally and by users to manipulate and query the
data.
–
Uses
set theory (as opposed to row processing) to process requests.
–
Limited
but flexible set of commands.
–
Free-form, 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)
Commands
classified by function:
–
Data
definition language (DDL) - define or change database structure(s)
CREATE
ALTER
DROP
–
Data
manipulation language (DML) - select or change data
INSERT
UPDATE
DELETE
SELECT
–
Data
control language (DCL) - control user access (e.g., GRANT, REVOKE)
–
Transactions
(e.g., COMMIT)