SPI_fname
SPI_fname — determine the column name for the specified column number
Synopsis
char * SPI_fname(TupleDescrowdesc, intcolnumber)
Description
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.) 
Arguments
- TupleDesc- rowdesc
- input row description 
- int- colnumber
- column number (count starts at 1) 
Return Value
 The column name; NULL if colnumber is out of range. SPI_result set to SPI_ERROR_NOATTRIBUTE on error.