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)