2.6 Cursors

The DBTools.h++ RWDBCursor class for Client-Library is implemented using
Client-Library ct_cursor() routines. These routines are subject to many restrictions:

Client-Library cursors are not scrollable; the only type of fetch supported is RWDBCursor::Next. Other types of fetch will result in an "Unsupported" error.
There must be a unique index on every table involved in every cursor operation. An error will result if any table does not have a unique index.
Since Client-Library supports server side cursors, updating a primary key column may result in problems such as multiple updates to the same row. In general, applications should only update nonprimary key columns. Neither this access library nor Client-Library prevents the application from updating a primary key column.
The application can control the number of rows fetched from the server to improve network performance. Refer to Section 2.15, "Contents of RWDBSystemHandle," for further details. Irrespective of the number of rows fetched from the server, calling RWDBCursor::fetchRow() will always return a single row and the rest of the rows are internally buffered within Client-Library.
In the case of multiple row fetches, the current row as perceived by the server is not the same as the current row as perceived by the application. Client-Library implements updates for the current row as perceived by the application.