1.decode的用法：
(select max(DECODE(logicSn,null,physicalid+1,logicSn+1)) from m_logic_channel where physicalid=#{physicalId}),
2.nvl的用法：
(select nvl(max(t.logicSn),0)+1 as num from m_logic_channel t),
oracle集锦
原文：http://www.cnblogs.com/dashen/p/4317916.html
