ODBC cursor characteristics

ODBC functions that execute statements and manipulate result sets, use cursors to perform their tasks. Applications open a cursor implicitly whenever they execute a SQLExecute or SQLExecDirect function.

For applications that move through a result set only in a forward direction and do not update the result set, cursor behavior is relatively straightforward. By default, ODBC applications request this behavior. ODBC defines a read-only, forward-only cursor, and SAP Sybase IQ provides a cursor optimized for performance in this case.

For applications that need to scroll both forward and backward through a result set, such as many graphical user interface applications, cursor behavior is more complex. What does the application when it returns to a row that has been updated by some other application? ODBC defines a variety of scrollable cursors to allow you to build in the behavior that suits your application. SAP Sybase IQ provides a full set of cursors to match the ODBC scrollable cursor types.

You set the required ODBC cursor characteristics by calling the SQLSetStmtAttr function that defines statement attributes. You must call SQLSetStmtAttr before executing a statement that creates a result set.

You can use SQLSetStmtAttr to set many cursor characteristics. The characteristics that determine the cursor type that SAP Sybase IQ supplies include the following:

• SQL_ATTR_CURSOR_SCROLLABLE – Set to SQL_SCROLLABLE for a scrollable cursor and SQL_NONSCROLLABLE for a forward-only cursor. SQL_NONSCROLLABLE is the default.
• SQL_ATTR_CONCURRENCY – Set to one of the following values:
  • SQL_CONCUR_READ_ONLY – Disallow updates. SQL_CONCUR_READ_ONLY is the default.
  • SQL_CONCUR_LOCK – Use the lowest level of locking sufficient to ensure that the row can be updated.
  • SQL_CONCUR_ROWVER – Use optimistic concurrency control, comparing row versions such as SQLBase ROWID or Sybase TIMESTAMP.
  • SQL_CONCUR_VALUES – Use optimistic concurrency control, comparing values.

For more information, see SQLSetStmtAttr in the Microsoft ODBC API Reference at http://msdn.microsoft.com/en-us/library/ms712631.aspx.

SQLAllocHandle( SQL_HANDLE_STMT, dbc, &stmt );
SQLSetStmtAttr( stmt, SQL_ATTR_CURSOR_SCROLLABLE,
      SQL_SCROLLABLE, SQL_IS_UINTEGER );