SPI_exec — execute a read/write command
int SPI_exec(const char *command, longcount)
   SPI_exec is the same as
   SPI_execute, with the latter's
   read_only parameter always taken as
   false.
  
const char * commandstring containing command to execute
long count      maximum number of rows to return,
      or 0 for no limit
     
   See SPI_execute.