New comment. This func/column things has always confused me.

/*
 *  parse function
 *  This code is confusing because the database can accept
 *  relation.column, column.function, or relation.column.function.
 *  In these cases, funcname is the last parameter, and fargs are
 *  the rest.
 *
 *  It can also be called as func(col) or func(col,col).
 *  In this case, Funcname is the part before parens, and fargs
 *  are the part in parens.
 *
 */
Node *
ParseFuncOrColumn(ParseState *pstate, char *funcname, List *fargs,
                  bool agg_star, bool agg_distinct,
                  int precedence)