Q120108: BUG: dBASE: SQL_ERROR w/ SQLExecute/SQLFreeStmt(SQL_CLOSE)

Article: Q120108
Product(s): Open Database Connectivity (ODBC)
Version(s): WINDOWS:1.0
Operating System(s): 
Keyword(s): kbBug kbISS
Last Modified: 27-JUL-2001

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The information in this article applies to:

- Microsoft Open Database Connectivity, version 1.0 
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BUG# ODBCDBASE: 2147 (1.01.1928)

SYMPTOMS
========

Calling SQLExecute, SQLFetch, and SQLFreeStmt/SQL_CLOSE in a loop on a prepared
statement can cause SQLExecute to return SQL_ERROR after several iterations. The
exact number of iterations before this error occurs depends on the number of
columns in the table. Users of MFC Database classes note that
CRecordSet::Requery followed by CRecordSet::MoveNext in a loop can cause the
same behavior.

To produce the problem, do the following with the ODBC dBASE driver:

  create table test (col1 char(5), col2 char(5))
     SQLPrepare: select * from test order by col2
     Loop
       SQLExecute
       SQLFetch
       SQLFreeStmt/SQL_CLOSE
     End Loop

At the 925th iteration of the above loop, SQLExecute will fail with SQL_ERROR.

Calling SQLError will return SQL_NO_DATA_FOUND. The number of iterations before
failure is dependent on the number of columns in the table. Here is some data
that will provide a rough idea of this dependency:

  Table with                 Iterations to SQL_ERROR
-----------------------------------------------------
   2 columns,    1 row                925
   2 columns, 1000 rows               925
   6 columns, 1000 rows               919
  10 columns, 1000 rows               599
  15 columns, 1000 rows               476
  17 columns, 1000 rows               399
  19 columns, 1000 rows               393

MFC Database class users will see the same behavior with the following loop,
after the same number of iterations as above:

     CRecordSet::Open, szSQLStr = select * from test order by col2
     Begin Loop
        CRecordSet::Requery
        CRecordSet::MoveNext
     End Loop

WORKAROUND
==========

Making either of the following two changes will work around the problem:

1. Remove the ORDER BY in the above SELECT statement (this is applicable to MFC
  users).

2. Do SQLExecDirect instead of SQLPrepare/SQLExecute. (This is not applicable to
  MFC users.)

STATUS
======

Microsoft has confirmed this to be a problem in ODBC dBASE Driver version
1.01.1928. We are researching this problem and will post new information here in
the Microsoft Knowledge Base as it becomes available.

Additional query words: 1.01.1928 Desktop Database Drivers Simba MSVC Visual C++

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Keywords          : kbBug kbISS 
Technology        : kbAudDeveloper kbODBCSearch kbODBC100
Version           : WINDOWS:1.0
Issue type        : kbbug

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