查询null以及length(),trim()使用

select * from stu_course t--  产品select * from stu_course t where t.is_publish='Y' and t.pid is null --  模块select t.*,length(trim(t.code)) lengthhh from stu_course t where t.is_publish='Y' and t.pid is not null and length(trim(t.code))>4--    select * from   student s  where     s.sno= 183  order by               ---    nvl(length(trim(s.sname)),0) asc -- 递增排序            -- nvl(attribute,default value) 当属性值为空时就将其值设默认值            -- length(attrbute) 得到字符串的长度            -- trim(attribute) 去掉字符的空格