<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Preparing ODBC</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REL="HOME" TITLE="FreeTDS User Guide" HREF="index.htm"><LINK REL="PREVIOUS" TITLE="Confirm the installation" HREF="confirminstall.htm"><LINK REL="NEXT" TITLE="Connection attributes" HREF="odbcconnattr.htm"><LINK REL="STYLESHEET" TYPE="text/css" HREF="userguide.css"></HEAD ><BODY CLASS="CHAPTER" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" ><SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > User Guide: A Guide to Installing, Configuring, and Running <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="confirminstall.htm" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="odbcconnattr.htm" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="PREPODBC" ></A >Chapter 4. Preparing ODBC</H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT ><A HREF="prepodbc.htm#ODBCBACKGROUND" >Background and Terminology</A ></DT ><DT ><A HREF="odbcconnattr.htm" >Connection attributes</A ></DT ><DT ><A HREF="dsnless.htm" >DSN-less configuration</A ></DT ><DT ><A HREF="odbcinionly.htm" >ODBC-only configuration</A ></DT ><DT ><A HREF="odbcombo.htm" >ODBC-combined configuration</A ></DT ><DT ><A HREF="odbcdiagnose.htm" >Troubleshooting ODBC connections</A ></DT ></DL ></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="ODBCBACKGROUND" >Background and Terminology</A ></H1 ><P >To connect to a database, a library such as <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > needs some information about the connection. Which server, and by <SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >server</I ></SPAN >, which IP address and port is do you mean? Which user is requesting the connection, and what authentication does he offer? Every database library needs a way to capture and convey that information. </P ><P >ODBC was conceived as a general interface definition, not tied to any particular database or access library. For that reason, ODBC also needs to know which driver to use with a given server. </P ><P >The original ODBC solution to this conundrum employed the <TT CLASS="FILENAME" >odbc.ini</TT > file. <TT CLASS="FILENAME" >odbc.ini</TT > stored information about a server, known generically as a <I CLASS="FIRSTTERM" >Data Source Name</I > (DSN). ODBC applications connected to the server by calling the function <CODE CLASS="FUNCTION" >SQLConnect(DSN, UID, PWD)</CODE >, where <TT CLASS="REPLACEABLE" ><I >DSN</I ></TT > is the Data Source Name entry in <TT CLASS="FILENAME" >odbc.ini</TT >, <TT CLASS="REPLACEABLE" ><I >UID</I ></TT > is the username, and <TT CLASS="REPLACEABLE" ><I >PWD</I ></TT > the password. Any and all information about the DSN was kept in <TT CLASS="FILENAME" >odbc.ini</TT >. And all was right with the world. </P ><P >The ODBC 3.0 specification introduced a new function: <CODE CLASS="FUNCTION" >SQLDriverConnect</CODE >. The connection attributes are provided as a single argument, a string of concatenated name-value pairs. <CODE CLASS="FUNCTION" >SQLDriverConnect</CODE > subsumed the functionality of <CODE CLASS="FUNCTION" >SQLConnect</CODE >, in that the name-value pair string allowed the caller to pass — in addition the the original <TT CLASS="LITERAL" >DSN</TT >, <TT CLASS="LITERAL" >UID</TT >, and <TT CLASS="LITERAL" >PWD</TT > — any other parameters the driver could accept. Moreover, the application can specify which driver to use. In effect, it became possible to specify the entire set of DSN properties as parameters to <CODE CLASS="FUNCTION" >SQLDriverConnect</CODE >, obviating the need for <TT CLASS="FILENAME" >odbc.ini</TT >. This led to the use of the so-called <I CLASS="FIRSTTERM" >DSN-less</I > configuration, a setup with no <TT CLASS="FILENAME" >odbc.ini</TT >. </P ><P >But <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > did not start out as an ODBC driver (remember db-lib and ct-lib), and has always had its own way to store server properties: <TT CLASS="FILENAME" >freetds.conf</TT >. When Brian added the <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > ODBC driver, he began by supporting the old <CODE CLASS="FUNCTION" >SQLConnect</CODE >, using <TT CLASS="FILENAME" >odbc.ini</TT > to describe the DSN. That choice complied with the expectations of the Driver Managers, and minimized the amount of duplicated information in the configuration files. But it can be a little confusing, too, because <TT CLASS="FILENAME" >odbc.ini</TT > in effect points to <TT CLASS="FILENAME" >freetds.conf</TT >. We call this configuration <I CLASS="FIRSTTERM" >ODBC-combined</I >, because it supports all three <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > libraries. </P ><P >With version 0.60, the <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > ODBC library started to see fuller implementation. The driver was made able to read the connection attributes directly from <TT CLASS="FILENAME" >odbc.ini</TT >, rather than leaning on <TT CLASS="FILENAME" >freetds.conf</TT >. For installations that don't need db-lib and ct-lib, this <I CLASS="FIRSTTERM" >ODBC-only</I > setup is simpler. </P ><P >More recently, <CODE CLASS="FUNCTION" >SQLDriverConnect</CODE > was added to <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN >. As described above, this function allows the application to specify connection attributes with reference to either, or neither, configuration file. It's your choice. In making that choice, keep the following terms clear in your mind: </P ><P ></P ><DIV CLASS="VARIABLELIST" ><P ><B >Important <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > ODBC terms</B ></P ><DL ><DT ><TT CLASS="LITERAL" >SERVERNAME</TT ></DT ><DD ><P >specifies the <TT CLASS="LITERAL" >[<TT CLASS="REPLACEABLE" ><I >dataserver</I ></TT >]</TT > entry in <TT CLASS="FILENAME" >freetds.conf</TT >. </P ></DD ><DT ><TT CLASS="LITERAL" >SERVER</TT ></DT ><DD ><P >specifies the real server i.e., the TCP/IP name of the machine hosting the database server. </P ></DD ><DT ><TT CLASS="LITERAL" >DSN</TT >, <TT CLASS="LITERAL" >Driver</TT ></DT ><DD ><P >In your connection string, you can decide to use a DSN entry in <TT CLASS="FILENAME" >odbc.ini</TT > using the <TT CLASS="LITERAL" >DSN</TT > attribute, or to specify the driver you want with the <TT CLASS="LITERAL" >Driver</TT > attribute.</P ></DD ></DL ></DIV ><P >In sum, <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > supports three ODBC three choices: </P ><P ></P ><DIV CLASS="VARIABLELIST" ><P ><B >ODBC configuration choices</B ></P ><DL ><DT >DSN-less</DT ><DD ><P ><SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >No</I ></SPAN > connection information is specified in <TT CLASS="FILENAME" >odbc.ini</TT >. Advantageous if you're using more of <SPAN CLASS="PRODUCTNAME" >FreeTDS</SPAN > than just the ODBC driver. </P ></DD ><DT >ODBC-only</DT ><DD ><P ><SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >All</I ></SPAN > connection information is specified in <TT CLASS="FILENAME" >odbc.ini</TT >, without the need for <TT CLASS="FILENAME" >freetds.conf</TT >. This is the <SPAN CLASS="QUOTE" >"traditional"</SPAN > ODBC setup. </P ></DD ><DT >ODBC-combined</DT ><DD ><P >Connection information maintained in <TT CLASS="FILENAME" >freetds.conf</TT >. <TT CLASS="FILENAME" >odbc.ini</TT > contains DSN entries that refer to dataserver names in <TT CLASS="FILENAME" >freetds.conf</TT >. </P ></DD ></DL ></DIV ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="confirminstall.htm" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.htm" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="odbcconnattr.htm" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Confirm the installation</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" > </TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Connection attributes</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
