（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