For Microsoft SQL Server, the DBTools.h++ class RWDBCursor is implemented using the capabilities of the SQL Server ODBC driver. DBTools.h++ cursors can be both sequential and scrollable. The access library specifies the cursor type by setting the statement attributes. The default cursor type implemented in this access library is SQL_CURSOR_KEYSET_DRIVEN.
Scrolling cursors and sequential cursors act differently with respect to large blob and string data. Scrolling cursors can not fetch large blob or string data of unlimited size. For scrolling cursors, memory is allocated and bound to receive the column data. Data is fetched only up to the size of the allocated memory. Member functions of class RWDBMsSqlLibEnvironmentHandle control the size of these memory allocations. Sequential cursors are not restricted in these ways.
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.
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