case when 使用

数据库中 null 和 ''  是不同的
select item_id,case   when   real_quantity = '' then '0' else real_quantity end as real_quantity from wlb_order_item_0000 where  id = 115002426
select item_id,case  when  real_quantity is null then '0' else real_quantity end as real_quantity from wlb_order_item_0000 where  id = 106820464


select item_id,case  when  real_quantity is null then '0' when   real_quantity = '' then '0' else real_quantity end as real_quantity from wlb_order_item_0000


case when then 中判断null的方法
http://blog.sina.com.cn/s/blog_6c61d6620100lofw.html

SQL利用Case When Then多条件判断
http://blog.sina.com.cn/s/blog_4e6dffee0100iwll.html

http://www.2cto.com/database/201203/124327.html