Determine the column name for the specified column number
char * SPI_fname(TupleDesc rowdesc, int colnumber)
SPI_fname returns a copy of the column name of the specified column. (You can use pfree to release the copy of the name when you don't need it anymore.)
TupleDesc rowdesc
input row description
int colnumber
column number (count starts at 1)
The column name; NULL if colnumber is out of range. SPI_result set to SPI_ERROR_NOATTRIBUTE on error.