Databases Reference
In-Depth Information
Some SQL Formalities
A database engine is the part of an RDBMS that actually stores and retrieves data
to and from the data files. The database engine is not very useful unless you can
send
SQL (Structured Query Language)
The industry-standard database lan-
guage used to query and manipulate the
data, structures, and permissions in a
relational database.
SQL (Structured Query Language)
commands to it and receive the results
from those SQL commands (if any).
“SQL” is usually pronounced “sequel,” but if you refer to “S-Q-L” in a conversation with
other database developers and DBAs, they will certainly know what you're talking about!
It is also important to separate the SQL commands from the command pro-
cessor itself. For example, Oracle's SQL*Plus client tool (available on virtually
any platform that the Oracle server itself runs on) has a number of other “built-
in” commands that look like SQL commands but operate only within the
SQL*Plus environment; these are called SQL*Plus commands. A SQL*Plus com-
mand may actually send many SQL commands to the Oracle server.
Tools for Running SQL
Most Oracle database environments consist of two, three, or more
. In the
simplest two-tier scenario, a database developer might be using SQL*Plus on a
Windows PC connecting to an Oracle database on a Linux server. More complex
environments may include a web server, application server, or authentication
server on a number of other servers in between the client and the database server.
Here, we will explore the various client-based tools that can be used to run
SQL, including SQL*Plus, iSQL*Plus, SQL*Plus Worksheet, third-party tools,
Open Database Connectivity (ODBC), Java Database Connectivity (JDBC), and
Oracle Call Interface (OCI).
tiers
tiers
Locations where different components of
an enterprise application system reside.
In a typical three-tier environment, the
client tier runs a thin application such as
a web browser, which connects to a mid-
dleware server that is running a web
server. The web server and its related
components typically manage the busi-
ness rules of the application. The third-
tier database platform controls access to
the data and manages the data itself.
This approach partitions the application
so that it is easier to maintain and seg-
regates the tasks into tiers that are best
equipped to handle a particular function.
SQL*Plus
SQL*Plus has been around as long as the Oracle RDBMS itself. It is the most
basic tool available for connecting to the database and executing queries against
the tables in a database. On Unix systems, it can be run in character-based mode,
even on a dumb terminal connected to the Unix system via a serial port.
The “Plus” part of SQL*Plus defines some of the extra functionality available
above and beyond executing SQL statements and returning the results. Some of
this functionality is proprietary to SQL*Plus and may not be available in non-
Oracle database environments. Here are some of the things you can do using
SQL*Plus:
Define headers and footers for reports.
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Rename columns in the report output.
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