Returns the name of a field (i.e., the column name) in the result set, or FALSE on error.
For "immediate" queries, or for dynamic columns, an empty string is returned.
Nota: The column index is zero-based, not one-based as in SESAM.
See also: sesam_field_array(). It provides an easier interface to access the column names and types, and allows for detection of "multiple fields".