（014）每日SQL学习：oracle下lag和lead分析函数

/*语法*/  
lag(exp_str,offset,defval) over()  
Lead(exp_str,offset,defval) over()  
--exp_str要取的列  
--offset取偏移后的第几行数据  
--defval:没有符合条件的默认值 

with x0 as 
(select '1'as aa ,to_date('2018-01-01','yyyy-mm-dd') as 日期 from dual
union all
select '2' as aa,to_date('2018-01-15','yyyy-mm-dd') as 日期 from dual
union all
select '3' as aa, to_date('2018-01-26','yyyy-mm-dd') as 日期 from dual )
select aa ,日期,
lead(日期,1,null) over (order by 日期),
lag(日期) over (order by 日期)
 from x0