int SPI_execute_plan(SPIPlanPtr plan, Datum * values, const char * nulls,
                     bool read_only, long count)   SPI_execute_plan executes a statement prepared by
   SPI_prepare or one of its siblings.
   read_only and
   count have the same interpretation as in
   SPI_execute.
  
      prepared statement (returned by SPI_prepare)
     
An array of actual parameter values. Must have same length as the statement's number of arguments.
An array describing which parameters are null. Must have same length as the statement's number of arguments.
      If nulls is NULL then
      SPI_execute_plan assumes that no parameters
      are null.  Otherwise, each entry of the nulls
      array should be ' ' if the corresponding parameter
      value is non-null, or 'n' if the corresponding parameter
      value is null.  (In the latter case, the actual value in the
      corresponding values entry doesn't matter.)  Note
      that nulls is not a text string, just an array:
      it does not need a '\0' terminator.
     
true for read-only execution
maximum number of rows to return, or 0 for no limit
   The return value is the same as for SPI_execute,
   with the following additional possible error (negative) results:
   
if plan is NULL or invalid, or count is less than 0
if values is NULL and plan was prepared with some parameters
   SPI_processed and
   SPI_tuptable are set as in
   SPI_execute if successful.