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Q116235: INFO: FoxPro Can Use SQL pass-through commands and ODBC

Article: Q116235
Product(s): Microsoft FoxPro
Version(s): WINDOWS:2.5,2.5a,2.5b,2.6,3.0,5.0,6.0; :
Operating System(s): 
Keyword(s): kbinterop kbDatabase kbvfp300 kbvfp500 kbvfp600 kbvfp260
Last Modified: 07-APR-2000

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The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0, 5.0, 6.0 
- Microsoft FoxPro for Windows, versions 2.5, 2.5a, 2.5b, 2.6 
- Microsoft FoxPro Connectivity Kit 
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SUMMARY
=======

FoxPro can use SQL pass-through commands and ODBC. This ability provides a
methodology for communicating with different data sources using a common syntax.

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

The FoxPro Connectivity Kit
---------------------------

FoxPro provides users with a "pass through" SQL capability. That is, you can pass
SQL commands to the ODBC data source by using SQL pass-through functions. This
capability is provided through 12 functions that are used to perform various
ODBC-related tasks.

Single and Multitier ODBC Drivers
---------------------------------

Current ODBC drivers fall into one of the following two categories: single- tier
or multitier.

- Single-Tier ODBC Drivers

  Single-tier drivers are used when the processing of SQL statements must be
  done by the driver itself; that is, when there is no back-end server to
  process the SQL statements. Thus, single-tier drivers are used to connect to
  dBASE, FoxPro, Paradox, Btrieve, Microsoft Access, Microsoft Excel, and text
  files.

  All of the Microsoft single-tier drivers use SIMBA.DLL and/or TXTISAM.DLL as
  the database "engine."

- Multitier ODBC Drivers

  Multitier drivers do not contain any processing capability and rely on a
  client-server DBMS to process SQL statements. SQL Server and ORACLE are two
  of the best known examples of a client-server DBMS.

ODBC Conformance Levels
-----------------------

There are two conformance levels for ODBC: API and SQL. The API conformance
levels are Core, Level 1, and Level 2. These specify varying degrees of API
support. Most current ODBC drivers are Level 1 and partially implement Level 2
features, such as scrollable cursors. (For a detailed discussion of this topic,
refer to the ODBC SDK documentation listed at the end of this article.)

The ODBC SQL conformance level is related to the SQL grammar implementation, and
falls into one of the following three categories:

 Minimum  - All ODBC drivers should implement this level.<BR/>
 Core     - Most ODBC drivers meet or exceed this level.<BR/>
 Extended - Many ODBC drivers partially implement this level.

The syntax for each level can be obtained from the ODBC SDK documentation, which
is listed at the end of this article.

Scalar Functions
----------------

ODBC has a number of functions built-in to allow language independence between
various database management systems. A list of these functions can be found in
the following Microsoft Knowledge Base articles:

  Q103576 SQL Server Time/Date Func Support for Connectivity Kit

  Q104342 SQL Server System Funcs Supported by the Connectivity Kit

ODBC functions are implemented with an ODBC "escape shorthand" syntax. This
syntax looks like:

  {fn ODBCFunction([Arguments])}

The following example shows how you can use the DBExec() function included in
FoxPro 2.x with the SQRT() ODBC function:

     lnResult=DBExec(dbHdle, "SELECT {fn sqrt(4)}","output")

In Visual FoxPro, use the following command:

     lnResult=SQLExec(dbHdle, "SELECT {fn sqrt(4)}","output")

To see an additional example of ODBC scalar functions, use the ClientServer
Wizard in the Professional edition of FoxPro version 2.6 for Windows to create
an outer join, and then examine the generated code.

REFERENCES
==========

"Microsoft ODBC 2.0 Programmer's Reference and SDK Guide," Microsoft Press

Additional query words: CK multi-tier

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Keywords          : kbinterop kbDatabase kbvfp300 kbvfp500 kbvfp600 kbvfp260 
Technology        : kbVFPsearch kbAudDeveloper kbFoxproSearch kbFoxPro260 kbFoxPro250 kbFoxPro250a kbFoxPro250b kbVFP300 kbVFP500 kbVFP600
Version           : WINDOWS:2.5,2.5a,2.5b,2.6,3.0,5.0,6.0; :
Issue type        : kbinfo

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