select ascii(A) A,ascii(a) a,ascii(0) zero,ascii( ) space from dual; 为何出错

执行语句
select ascii(A) A,ascii(a) a,ascii(0) zero,ascii( ) space from dual; 为何出错
在行 1 上开始执行命令时出错:
select ascii(A) A,ascii(a) a,ascii(0) zero,ascii( ) space from dual
命令出错, 行: 1 列: 43
错误报告:
SQL 错误: ORA-00909: 参数个数无效
00909. 00000 - "invalid number of arguments"
*Cause:
*Action: