有关oracle max函数的疑惑,求解!
表结构如下:
create table M_PROJECT_WORK_FINISH
(
WORK_FINISH_ID VARCHAR2(31) not null,
WORK_ITEM_ID VARCHAR2(31),
PROJECTID VARCHAR2(31),
STATUS VARCHAR2(31)
)
select * from M_PROJECT_WORK_FINISH where projectid='2010-3201-0301-000007'
查询结果如下:
1 754 2 2010-3201-0301-000007 1
2 755 9 2010-3201-0301-000007 0
3 756 5 2010-3201-0301-000007 1
select max(to_number(work_item_id)) as max from m_project_work_finish where projectid='2010-3201-0301-000007' 的查询结果是9
为什么如下的sql语句查询就有变成空值了呢:
select max(to_number(work_item_id)) as max from m_project_work_finish where projectid='2010-3201-0301-000007' and status='1'
求解!