SPI_gettype — return the data type name of the specified column
char * SPI_gettype(TupleDescrowdesc, intcolnumber)
   SPI_gettype returns a copy of the data type name of the
   specified column.  (You can use pfree to
   release the copy of the name when you don't need it anymore.)
  
TupleDesc rowdescinput row description
int colnumbercolumn number (count starts at 1)
   The data type name of the specified column, or
   NULL on error.  SPI_result is
   set to SPI_ERROR_NOATTRIBUTE on error.