DOCUMENT:Q101520  30-JUL-2001  [odbc]
TITLE   :INF: SQLDescribeCol Limitation on Meta Data
PRODUCT :Open Database Connectivity (ODBC)
PROD/VER:
OPER/SYS:
KEYWORDS:

======================================================================
SUMMARY
=======

SQLDescribeCol in the ODBC API and SAG's Call Level Interface Specification is
intended to return meta data about a column in a results set. However, it does
not return table names as part of this meta data. This article discusses how
this limitation stems from SQL92, and also how applications can work around this
limitation.

MORE INFORMATION
================

SQLDescribeCol returns the column names of the results set in szColname.
However, when two columns in a results set have the same name (for example, by a
join between 2 tables), it does not return the table name along with the column
name to differentiate the two similarly named columns.

This limitation arises from SQL, more specifically SQL92, which addresses this
issue in Subclause 7.4, Syntax Rule 1b) on the 'From Clause':

   If the <from clause> contains more than one <table reference>
   with no intervening <derived table> or <joined table>, then the
   descriptors of the columns of the result of the <from clause> are the
   descriptors of the columns of the tables identified by the <table
   reference>s, in the order in which the <table reference>s appear in
   the <from clause> and in the order in which the columns are defined
   within each table.

Given the above rule, the following SQL example should clarify this:

   // Table1 has a column 'address', and so does Table2
   select * from Table1, Table2

The 'address' column can be differentiated as being from Table1 or Table2
depending on its position in the results set. The 'address' column from Table1
will always come before the 'address' column in Table2.

Additional query words: 1.00

======================================================================
Keywords          :  

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 2001.