SPI_modifytuple — create a row by replacing selected fields of a given row
HeapTuple SPI_modifytuple(Relationrel, HeapTuplerow, intncols, int *colnum, Datum *values, const char *nulls)
   SPI_modifytuple creates a new row by
   substituting new values for selected columns, copying the original
   row's columns at other positions.  The input row is not modified.
   The new row is returned in the upper executor context.
  
   This function can only be used while connected to SPI.
   Otherwise, it returns NULL and sets SPI_result to
   SPI_ERROR_UNCONNECTED.
  
Relation relUsed only as the source of the row descriptor for the row. (Passing a relation rather than a row descriptor is a misfeature.)
HeapTuple rowrow to be modified
int ncolsnumber of columns to be changed
int * colnum      an array of length ncols, containing the numbers
      of the columns that are to be changed (column numbers start at 1)
     
Datum * values      an array of length ncols, containing the
      new values for the specified columns
     
const char * nulls      an array of length ncols, describing which
      new values are null
     
      If nulls is NULL then
      SPI_modifytuple assumes that no new values
      are null.  Otherwise, each entry of the nulls
      array should be ' ' if the corresponding new value is
      non-null, or 'n' if the corresponding new 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.
     
   new row with modifications, allocated in the upper executor
   context, or NULL on error
   (see SPI_result for an error indication)
  
   On error, SPI_result is set as follows:
   
SPI_ERROR_ARGUMENT       if rel is NULL, or if
       row is NULL, or if ncols
       is less than or equal to 0, or if colnum is
       NULL, or if values is NULL.
      
SPI_ERROR_NOATTRIBUTE       if colnum contains an invalid column number (less
       than or equal to 0 or greater than the number of columns in
       row)
      
SPI_ERROR_UNCONNECTEDif SPI is not active