On Sat, 12 Jun 1999, Thomas Lockhart wrote:
> I like it! :)
>
> Of course, if I include it in the docs then it would be much more
> effective if I also include the previous 20 mail messages on the
> subject...
>
> - Thomas
Ok...ok! I sheared off abit of the fluff and here it is...provided
it meets with everyone's approval you're free to do with it what you
will.
Cheers,
Tom
-------------------------------------------------------------
SQL subsets - QUERIES, DML, DDL and DCL
---------------------------------------
The original query language that accompanied IBM's System R database
was known as SEQUEL (Structured English QUEry Language). IBM
later truncated the name to SQL - pronounced either as sequel
or as the phonetic eS-Que-eL. SQL has one basic operation and
3 subsets:
The QUERY - SQL has one primordial operation known as a QUERY.
'SELECT' is the verb in the basic SQL query. Queries can become rather
complex and may include elements of DML (Data Manipulation Language).
Queries may also access tables that contain TRIGGERs and RULEs
thus invoking more complex database operations. In its most elemental
form, however, a SELECT statement is a simple QUERY.
DML - the Data Manipulation Languge subset of SQL - is composed of
INSERT INTO, UPDATE and DELETE FROM statements. DML manipulates data
(altering it) while SELECT, at least in its purest form, does not.
DDL - the Data Definition Language subset of SQL - is a collection of
statements that create and destroy database objects. It includes
CREATE TABLE, CREATE SEQUENCE, CREATE INDEX and similar statements. It
also includes the destructive counterparts: DROP TABLE and so on.
(Unfortunately DROP ACRONYM is apparently yet to be implemented.)
DCL - the Data Control Language subset of SQL - is that part of the SQL
language that controls user access. It contains the GRANT and REVOKE
statements which govern permissions.
------- North Richmond Community Mental Health Center -------
Thomas Good MIS Coordinator
Vital Signs: tomg@ { admin | q8 } .nrnet.org Phone:
718-354-5528 Fax: 718-354-5056
/* Member: Computer Professionals For Social Responsibility */
------- North Richmond Community Mental Health Center -------
Thomas Good MIS Coordinator
Vital Signs: tomg@ { admin | q8 } .nrnet.org Phone:
718-354-5528 Fax: 718-354-5056
/* Member: Computer Professionals For Social Responsibility */