SPI_cursor_fetch — fetch some rows from a cursor
void SPI_cursor_fetch(Portalportal, boolforward, longcount)
   SPI_cursor_fetch fetches some rows from a
   cursor.  This is equivalent to a subset of the SQL command
   FETCH (see SPI_scroll_cursor_fetch
   for more functionality).
  
Portal portalportal containing the cursor
bool forwardtrue for fetch forward, false for fetch backward
long countmaximum number of rows to fetch
   SPI_processed and
   SPI_tuptable are set as in
   SPI_execute if successful.
  
   Fetching backward may fail if the cursor's plan was not created
   with the CURSOR_OPT_SCROLL option.