oracle中查询value为空的日期

在oracle中,我想查找一条zhd_riqi值为空的记录,可是不知道如何来写这条语句,那位大虾帮忙一下
select * from tbl_zhd where zhd_riqi = null; ==========这个句子找不到记录
[128 byte] By [gfik_blue] at [2008-5-20]
# 1
select * from tbl_zhd where zhd_riqi is null
fatpig521-瘦驼 at 2007-10-22 > top of Msdn China Tech,其他数据库开发,SQL Anywhere Studio...