<Chapter Id="odbc">
<DocInfo>
<AuthorGroup>
<Author>
<FirstName>Tim</FirstName>
<Surname>Goeke</Surname>
</Author>
<Author>
<FirstName>Thomas</FirstName>
<Surname>Lockhart</Surname>
</Author>
</AuthorGroup>
<Date>1998-08-25</Date>
</DocInfo>

<Title><acronym>ODBC</acronym> Interface</Title>

<Para>
<Note>
<Para>
Background information originally by
 <ULink url="mailto:tgoeke@xpressway.com">Tim Goeke</ULink>
</Para>
</Note>

<Para>
<acronym>ODBC</acronym> (Open Database Connectivity) is an abstract 
<acronym>API</acronym> 
which allows you to write standard "ODBC" applications.
<acronym>ODBC</acronym> provides a product-neutral interface 
between frontend applications and database servers,
allowing a user or developer to write applications which are portable among servers.

<Sect1>
<Title>Background</Title>

<Para>
The <acronym>ODBC</acronym> <acronym>API</acronym> matches up 
on the backend to an <acronym>ODBC</acronym>-compatible data source.
This could be anything from a text file to an Oracle or 
<productname>Postgres</productname> <acronym>RDBMS</acronym>.

<Para>
The backend access come from <acronym>ODBC</acronym> drivers, or vendor specifc drivers that
allow data access.   <productname>psqlODBC</productname> is such a driver, along with others that are
available, such as the OpenLink <acronym>ODBC</acronym> drivers.

<Para>
Once you write an <acronym>ODBC</acronym> application, you SHOULD be able to connect to ANY
back end database, regardless of the vendor, as long as the database schema
is the same.

<Para>
For example. you could have <productname>MS SQL Server</productname>
 and <productname>Postgres</productname> servers which have
exactly the same data.  Using <acronym>ODBC</acronym>, your Windows app would make exactly the
same calls and the back end data source would look the same (to the windows
app).

<para>
<ulink url="http://www.insightdist.com/">Insight Distributors</ulink> provides active and ongoing
support for the core <productname>psqlODBC</productname> distribution. They provide a
<ulink url="http://www.insightdist.com/psqlodbc/"><acronym>FAQ</acronym></ulink>, ongoing development
on the code base, and actively participate on the 
<ulink url="mailto:interfaces@postgresql.org">interfaces mailing list</ulink>.

<sect1>
<title><productname>Windows</productname> Applications</title>

<Para>
In the real world, differences in drivers and the level of <acronym>ODBC</acronym> support
lessens the potential of <acronym>ODBC</acronym>:

<SimpleList>
<Member>
Access, Delphi, and Visual Basic all support <acronym>ODBC</acronym> directly.

<Member>
Under C++, such as Visual C++, you can use the C++ <acronym>ODBC</acronym> <acronym>API</acronym>.

<Member>
In Visual C++, you can use the CRecordSet class, which wraps the 
<acronym>ODBC</acronym> <acronym>API</acronym>
set within an MFC 4.2 class.  This is the easiest route if you are doing
Windows C++ development under Windows NT.
</SimpleList>

<Para>
If I write an app for <productname>Postgres</productname> 
can I write it using <acronym>ODBC</acronym> calls
to the <productname>Postgres</productname> server, or is that only when another database program 
like MS SQL Server or Access needs to access the data?

<Para>
Again, the <acronym>ODBC</acronym> <acronym>API</acronym> set is the way to go.
You can find out more at
Microsoft's web site or in your Visual C++ docs (if that's what you are using.)

<Para>
Visual Basic and the other RAD tools have Recordset objects that use <acronym>ODBC</acronym>
directly to access data.  Using the data-aware controls, you can quickly
link to the <acronym>ODBC</acronym> back end database (<Emphasis>very</Emphasis> quickly).

<Para>
Playing around with MS Access will help you sort this out.  Try using
File->Get External Data

<Para>
<Tip>
<Para>
You'll have to set up a DSN first.
</Para>
</Tip>

<!--
<Para>
<Tip>
<Para>
The <productname>Postgres</productname> datetime type will break MS Access.
</Para>
</Tip>
-->

<sect1>
<title><productname>Unix</productname> Applications</title>

<para>
<productname>ApplixWare</productname> has an <acronym>ODBC</acronym> database interface
supported on at least some platforms. <productname>ApplixWare</productname> v4.4.1 has been
demonstrated under Linux with <productname>Postgres</productname> v6.4 
using the <productname>psqlODBC</productname>
driver contained in the <productname>Postgres</productname> distribution.

<sect2>
<title>Configuration Files</title>

<para>
The <filename>~/.odbc.ini</filename> contains user-specified access information 
for the <productname>psqlODBC</productname>
driver. The file uses conventions typical for <productname>Windows</productname> 
Registry files, but despite this
restriction can be made to work.

<para>
Here is an example <filename>.odbc.ini</filename> file, 
showing access information for three databases:

<programlisting>
[ODBC Data Sources]
DataEntry = Read/Write Database
QueryOnly = Read-only Database
Test = Debugging Database
Default = Postgres Stripped

[DataEntry]
ReadOnly = 0
Servername = localhost
Database = Sales

[QueryOnly]
ReadOnly = 1
Servername = localhost
Database = Sales

[Test]
Debug = 1
CommLog = 1
ReadOnly = 0
Servername = localhost
Username = tgl
Password = "no$way"
Port = 5432
Database = test

[Default]
Servername = localhost
Database = tgl
Driver = /opt/postgres/current/lib/libpsqlodbc.so

[ODBC]
InstallDir = /opt/applix/axdata/axshlib
</programlisting>

<para>
For Applix, here is an example ~/axhome/macros/login.am file:
<programlisting>
macro login
        set_set_system_var@("sql_username@","tgl")
        set_system_var@("sql_passwd@","no$way")
endmacro
</programlisting>

<sect1>
<title>Supported Platforms</title>

<para>
<productname>psqlODBC</productname> has been built and tested 
on <productname>Linux</productname>. There have been reports of success 
with FreeBSD and with Solaris.

</Chapter>

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